Because these two organizations are trying to help couples fulfill a mitzvah.
HaQer has a good point, and it can be taken further almost ad infinitum.
People who can’t afford a real Shabbos could technically buy a few whole loaves of bread, make kiddush and hamotzi on them, and they’ve fulfilled the mitzvah of seudos on Shabbos. Does that mean that organizations trying to give needy families a real Shabbos aren’t worthy of our donations?
The same thing goes for medical relief organizations. Not everything they do is pikuach nefesh. Should we say, hey, if these people can’t afford it, why should we have to pay for their medical needs?
Couples can get married without having a traditional wedding. All you need is a chosson, kallah, two eidim and a mesader kiddushin. Just because they’ve decided that they want to have a semblance of a real wedding with music, a seudah and dancing, does that mean the tzibbur has to pay for it?
I would like to honor your request about not telling you that you’re being insensitive. I think I would be able to, if not for your comment about the pool, the requisite “lehavdil” notwithstanding.
Perhaps you are not yet married, or, if you are, you have never undergone the yissurim of fertility/secondary infertility, and perhaps you don’t even know anyone who has. It would seem to me that, if you had any inkling of the excruciating pain these couples go through, you would never have been able to use installing a pool as a legitimate mashal.
If you personally have a question about these organizations, the best thing to do would be to ask your personal Rav if you should donate.