In the era of linear TV, the masses had to watch what the networks put in front of them. People had to watch whatever was available in the broadcast medium of their choice (air/cable/satellite). Channel flipping meant that the networks had a brief moment to expose themselves to viewers, and maybe even hook them with those repetitive post-commercial recaps.
But non-linear television means that the network execs can fuck right off because people will watch whatever they want, whenever they want, on the subscription service they want. The fragmentation is real.
The homescreen ads present themselves as a rare chance for channel producers to say "hey! come look at our amazing content!". Right before a viewer fires up Netflix or whatever.
(On a personal note, those overly loud and obnoxious homescreen ads are fucking annoying and usually turn me off from whatever the hell is being advertised. Turning on my TV should be a source of joy and relaxation, not a a desperate desire to pull up Netflix as fast as humanly possible. I'm also certain that in the future when all of our smart TVs have 128-core RISC-V CPUs with 16GB of RAM and can run k8s, TV software producers will intentionally slow down the loading of apps so viewers are forced to watch the homescreen ads.)