Our club picked a 900 page book and 4 people quit in one meeting
I looked it up after we voted and saw the average book club pick runs about 350 pages, so I'm wondering if your groups have page limits or if you just let someone pick a brick and watch everyone scramble.
That 350 average is a bit misleading since it gets pulled down by all the short novels and novellas people vote in. Plenty of clubs out there are reading 500 to 600 page books without anyone blinking, think Ken Follett or Donna Tartt or anything by Stephen King. The real killer with a 900 pager is fitting it into one month, since most clubs meet every 4 weeks and that's about 30 pages a day if you don't fall behind. People quit because of the schedule, not the page count. Give them 6 or 8 weeks for a brick and half those folks probably stick around.