I'm pretty sure it's just more options, mainly social media. Everyone I know has plenty of leisure time to browser stuff on their phone, but book reading is a distant thought for most.

Yeah, I really doubt people would read much more if they worked less. You need a combination of literacy and a longer attention span, and these qualities are strengthened by reading more often. If you go forever without reading a book, it's harder to read through long books with advanced language that you used to be able to read effortlessly—and this is not because you don't understand the language, but because you lack the willpower to continue, since it's a bit mentally tiring to if you've fallen out of practice. At least, that's my experience, having gone through long stretches of time without reading.

So, based on my own experience, I think most people who don't read actually wouldn't be able to read more given more time. They would need to practice reading books that are easy on their level (both literacy level and attention-span level), and gradually advance to longer and more difficult books to read.