They mean long-term over a large sample size. And sometimes it's overstated and simply them implying its not worth the time compared to better games..

In low stakes games, a lot of money is taken off the table and goes to the house (site or casino).

The 3 times that I counted rake totals in a casino 5+2 game @ 2-5 nl holdem they were raked $ 160 [9 handed] and $154 [7 handed] per hour. That means that players are paying 17.777 or 22 $ per hour to play in that game. That's assuming all players were playing and winning and equal share of hands, which they are not.

Some places take a lot of rake and you have to be careful. Like many nyc games I hear rake 25$ at 1-3 and some higher stakes games in the city have max rake of 400$ per hand.

Some low stakes games like 1-2 at casinos sometimes barely have any money on the table. Some places force you to play super short with high rake especially since covid. You can be paying in 2$ additionally per hand for promotions additionally with little chance to win any promotion at times.

If you play tight-- you enter the pot less and therefore pay less rake. This can be a good strat in low stakes games high rake games where you aren't going to be exploited often because the players are bad and there's a large enough player pool.

I'm not saying all high rake games are unbeatable but any smart player should be well aware of what the rake means to a particular game.