Whatever the reason a person may "just want to be friends" is their reason.  You can only control your own actions and reactions.  Don't give up on friendships or the desire for a relationship.  Treat others in a way that honors God, not in spite or malice.  Care for your sisters in Christ in every relationship.

Be strong and take heart, all you who hope in the Lord (Psalms 31:24).

SHE SAID:  I love/hate the "just friends" qualifier.  Love, because it's something that is such a sign of our times and worth some commentary.  And hate, because it can be easily misused and misinterpreted.

Boiling it down, why do women respond by saying they want to be "just friends" with you?  As a woman, I know why I have said this before.  Because I have been approached by someone with whom I'm not interested in anything more than friendship and feel like I must define the relationship and make this clear upfront, so that the other party will know that I do not have romantic feelings toward him.

Perhaps some of your female friends feel the same way.  And even at that, saying you want to be "just friends" with someone certainly does not mean that romantic feelings could never develop over time.  But sometimes a man already has strong feelings for a woman, and she is just not there yet.  Or maybe she never will get there.  Only time will tell.  Thus, a woman may feel that she is being courteous by telling a man upfront how she feels.  Maybe in her mind it's like putting a sticky note you both can see on your relationship ("Don't forget!  We're just friends.").

That is how I have felt every time I have shared the "just friends" message with someone who I thought was interested in me (beyond friendship).  I knew I wasn't interested (romantically), and I indicated that spending time together as "just friends" was only what I would agree to doing.  But that was all.  Capice?

Some of the "ills" you refer to can be quite annoying.  However, I also think it would be unfair to say every unreturned phone call or every time someone's words don't seem to match up with their actions that there is something wrong or that the other party (you, in this case) has a right to be offended.  I would argue that these "ills" must be examined on a case-by-case basis, and that we also must factor in a margin for error and misinterpretation on your part (‘cause we've all read some situations wrong before, right?).

For example, perhaps a woman has not returned an e-mail or a phone call, because she is trying not to lead someone on.  Or perhaps an interested party keeps e-mailing and e-mailing and e-mailing.  Or calling and calling and calling.  By not answering, then a message (albeit a firm one) is sent.  She does not want to encourage an interested party's pursuit.  If you need further proof or need to do more recon work, take note of how a woman you are interested in (but who may not be interested romantically in you) acts around you in person.  Does she keep a distance from you and does not seek to engage with you in conversation?  That could be a clue as to how she feels about you.  (Yes, she could also be shy, and that's where friends will come in to play—if she likes you, they will know and it won't be long before they'll let you know.).

I agree with you that it is frustrating to run up against the "just friends" barrier—especially when you are interested in someone.  First, we must acknowledge that there just might not be any chemistry there, and if so then we must take the uninterested party at his or her word and respect that decision and that boundary. 

Also, I believe it's possible that women are just as commitment-phobic as men.  Men seem to always get tagged with this label, but I believe there are plenty of women who are also afraid of relationships and emotional intimacy with someone else (even though they may not be conscious of this in themselves).  Yes, many of us have been burned by romantic relationships and even by familial relationships or by divorce.  We have some residual trust issues to continually work through, and we aren't so quick to hand over our hearts as others.  But then, some of us are too over-protective of our hearts—which means we are walking a fine line between living in fear and trusting the Lord as he leads and shows us who he is guiding us toward (if he is).

Finally, it's possible that you just haven't met the right person.  Perhaps God is protecting you from unhealthy or unbenefical relationships right now and is blocking these potential opportunities by surrounding you with women who want to be "just friends" with you.  I think it's possible.  He may want you to not be in a relationship right now and to be less distracted and more available to work on yourself or your relationship with him.  I know for me, in seasons of singleness (when I have not been dating someone), I have been more attuned to God and what he is saying to me in my life.  Yes, it can be lonely and frustrating at times, but I can see how I have grown spiritually and how my relationship with the Father has deepened and enriched my walk when my time and devotion are freed up to focus solely on him.