I was like this for a long time and what really got me back into reading long books (currently reading the Stormlight Archive, 1000+ pages per book!) was reading some real "trash" to get back into reading. For me, it was reading a whole bunch of Michael Crichton books. I love his work, it's so dry and technical but more than that, they are silly with generally 2 dimensional characters, but have interesting plots and story beats and are generally really thrilling, but easy reading. I suppose you could say the same for Dan Brown books....

Honestly, reading Jurassic Park, The Lost World, Congo, Prey, Shphere etcetc got me back into reading in a big way and I really can't reccomend some "easy reading" enough to reignite your interest.

If you;re looking for a single authors works to get into as well, read the Discworld series, starting with Guards Guards!