Mobile carriers have only a limited number of IPs available, but they also have millions of customers. How can they make every of their customers browse the internet? They assign the same IP to more users at the same time.
Vodafone Italia, for example, runs all of its mobile network using only two subnets, 5.90.x.x and 37.159.x.x. Each of them has 65,536 IPs, for a total of 131,000.
At 31st March 2018 they have 22,284 millions clients = 170 customers on each IP.
This is a big advantage when using mobile IPs for social networks automation. The platform can't blacklist the subnets (as very often happens with Datacenter proxies) because it's IPs are being used by legit users.Datacenter/VPS/cloud subnets are being constantly banned since only spammers and zero legit users use them and for this reason you can't like or follow by default using their proxies most of the times.