Lots of reasons. I'm sure Paul can comment with his own views on this.
I tried camping on early trips to Mexico -Cent. America. In crowded areas camping can be a problem. Parts of Cent. Am. are quite dense, hard to get away from people.
Parts of the Caribe side can be mellow and some good camping can be had at organized areas. But be careful about walking away from your camp site for too long. You are always a target ... even in paradise. I'm not always a fan of Wild Camping ... but many do it no problems. I don't like to leave my stuff unattended ... so in some cases you can become a prisoner of your camp site.
Camping takes extra time, shortens your riding day ... you ALWAYS need to stop riding with daylight left. Setting up in the dark if not much fun. Then, you've got to cook ... and clean up. In the AM same routine: more cooking, cleaning, re-packing. If you're up at first light ... you might get on the road by 8:30 or 9 am. After riding all day some may not have the energy left to do all that is required to camp and cook. A lot of extra work.
In the 1960's Mexico had more camping at tourist beaches ... but not much these days. ALL BIG Hotels. In remote inland areas some camping can be found ... but it's best if you know where you are, who's land your on. Never pick a spot in the dark.
On later trips I stopped camping. I preferred staying in towns - villages and collected tips from other travelers about places to stay. Worked well for me: More contact with locals meant learning more Spanish ... learning more about the culture.
Camping can be isolating ... I've seen many Euros doing this, staying to themselves, not speaking Spanish, living in the Bush, not bathing much, eating out of cans, carrying their own bread, cheese and stuff, having almost no contact with locals. Works for some.
Being in town forces you to interact.
I prefer eating at local markets /restaurants, having more contact with local folk. Some travelers get exhausted by this and long for isolation. To each their own.
Others follow the Gringo trail and stay at Hotels or Hostels where ALL the patrons are other English speaking travelers. Many of the younger crowd are there to Party and get high ... some are on vacation from College. All good I guess.
I did this myself for a while (30 years ago) as it's always good meeting others on the road to learn what's coming up regards roads, border crossings, police issues, political stuff and good tips on places to stay and sites to see.
If you have the time ... camping can be good. It gets VERY good in Southern Argentina and Southern Chile ... which is sort of like Northern California. But requires carrying a lot of extra gear and allowing shorter riding days and doing the extra work.