I think at the end of the day, it's because the modern way of designing things is just easier for developers.
I remember when that started taking off; it was honestly kind of a godsend because one of the laziest way of doing things suddenly became associated with professionalism. On the other hand, it's getting pretty bland as a consumer now that every site is doing it.
Compared to images as buttons of the 2000s, something adjacent to material design seriously cuts down on the number of graphical assets necessary for develop anything. Even games seem to follow that trend: compare Crusader Kings 2 vs Crusader Kings 3, with image buttons vs a general UI toolkit in the two games.
I remember when that started taking off; it was honestly kind of a godsend because one of the laziest way of doing things suddenly became associated with professionalism. On the other hand, it's getting pretty bland as a consumer now that every site is doing it.
Compared to images as buttons of the 2000s, something adjacent to material design seriously cuts down on the number of graphical assets necessary for develop anything. Even games seem to follow that trend: compare Crusader Kings 2 vs Crusader Kings 3, with image buttons vs a general UI toolkit in the two games.