Makes sense. Biden wasn't able to keep up with a demanding campaign schedule either, it was one of the big reasons he needed to withdraw. Trump is around the same age, and frankly it's just a lot to ask of an elderly person.
It's not like he'll cancel his rallies, he recreationally enjoys those. So the interviews are what get dumped.
The rallies also offer no challenge. Interviews, potentially, have tough questions or a hostile audience. He enjoys the rallies because it’s just bunch of people propping up his ego without giving one shit about what he says.