why? I do not even know how to search why is it bad to use css background for background images in this context.

Maybe if you elaborate a bit more about why do you think it's broken. Is it hard to develop? Aren't you making enough profit of it? Is it used for bad purposes? To many frameworks to few original work? I think web development is healthy comparing it with mobile apps development, in terms of profit and tools available. But it's just a narrowed perspective.

Some time ago the purpose of the section give it a name. 'Featured', 'Call to action', 'Main content', etc... But nowadays some frameworks just give a name with no reason. I mean is like call a navigation section: 'Villian', or 'Nonsense'

I also wonder why so much hate for the old and reliable jQuery. After read the comments below notice that some of the most experimented devs, have some respect for jQuery besides the bad practices and the poor performance. But trying to catch up with new, shining and shrewdly named frameworks I found some trends that are equaly hateful, from angular, to vue, all of them appears to put all the eggs on performance but little or none on friendlyness. Thats why (I think) so many novice users are reluctant to change. The old boy stills there doing the job. From my point of view (as a designer who happens to do some web) there are anything close to jquery to solve basic interactions. There are some good libraries like zepto.js that do a great job, so if you are like me trying to make the transition it may be helpful.