You'd be surprised. A few years ago now there were plenty of users using the most popular brands, and the IP ranges were often overlapped.
There is a slight difference between using the exact same IP and IPs that overlap randomly
Let's say we have 3 users and they use
Monday
User A: 2.7.232.198
User B:179.184.16.236
User C:198.53.253.236
Tuesday
User A: 179.184.16.236
User B:198.53.253.236
User C:83.174.54.56
Wednesday
User A: 198.53.253.236
User B:158.158.7.213
User C:97.169.204.15
well you get the idea, I would not think of this as highly suspicious, suspicious a bit yes, but not alarming.
Then you have the same users
Monday
User A: 2.7.232.198
User B:2.7.232.198
User C:2.7.232.198
Tuesday
User A: 179.184.16.236
User B:179.184.16.236
User C:179.184.16.236
and so on the entire week.
common, I would bet my house on those accounts being run by the same guy.

I'm using a paid VPN and because some website I use is run by complete idiots so I need to actually use the same servers with close IP *.*.*.x when I log in, you can't imagine how hard is to find them available every time and under 90% usage and those are premium servers, not free.