CSGO maps are notorious for not being optimized for PCs. A few years ago, valve reasoned that the only reason they did not want to give 128 tick servers was due to the data with them. They realized that the vast majority of the player base did not have better PC and having 128 tick servers would make the game unplayable on several PCs. As a result matchmaking stayed on 64 tick while third-party servers came up with 128 tick servers.
Valve said they don't have 128 tick MM servers because most casual players computers can't utilize more than 64 tick anyways. So most casual players have bad PCs so lets make every new map run worse and worse and never optimize the game for better frames #logic
— nouns SEMPHIS (@semphisss) January 17, 2018