I do a LOT of volunteer work for the Humane Society of Missouri at Longmeadow Rescue Ranch which is for rescued horses, pigs, goats, ducks - pretty much all farm animals. We see some of the worst horrors you can imagine. Our only source of money, other than a few grants, is donations. We get no public money at all. So, a couple of times a year they have a telethon on local TV and for the holidays we take some of our Barn Buddies (this last time was a couple of miniature horses named Teddy and Ritz) down to the station for a segment on giving Barn Buddy sponsorships as gifts.
I am not a huge fan of the Humane Society of the US or of UNICEF and do not donate to either of them. I don't watch much television, so I don't see these ads, but it would annoy me to no end if they did it constantly too. I would be very careful of donating to anything - check them out thoroughly. There are so many, many scams out there.
And to answer your question of "why," this is an example of why we ask for donations a couple of time a year. The looks on the faces of these little kids with their new pony make all the work and heartbreak worthwhile.
Tweety