No trend here-just something you've stumbled upon as buffets have been around for decades. People have differing opinions about them. Foremost is the variety you get for your money and that there is no limit to how much you can get. I've often heard some folks hate buffets because they feel like it's one big troff under a roof. Some see buffets as dirty since you don't have a small wait staff handling the food utensils but ALL of the customers instead-often throwing the utensil in the food after handling it, throwing it on the serving table, etc.-you name it---different ways that can introduce a transfer of germs. So no, you've just discovered a small sector of the restaurant business that you may or may not like. Myself, I don't like to make a habit of going to them (for the reasons above) but I love the variety and that I can control the portions myself. Having said all that, I am extra cautious with what I'm getting and how I use the utensils there.
Honey - there have been all-you-can-eat restaurants/buffets for at least a hundred years. It is hardly what I would call a new trend nor are regular service restaurants in any jeopardy.
Besides, the food they serve at those is sub-par at best. I doubt the entirety of humanity is suddenly going to all want poor quality food served buffet style, any time soon.