Battle passes yes. Often battle passes will have a free progression tier and a paid one. But seasons are often just made so people have an incentive to come back to the game. In the case of diablo3 and path of exile for example a new season will mark a new patch that changes game mechanics (buff certain builds, Nerf others or through new items enable builds that weren’t possible before). To play a season you have to start a new character so that gives you the incentive to try a new build which Poe has plenty of. Seasons will also introduce a mechanic only available in the season that make playing it feel unique and different. Season mechanics often require a lot of Dev work and are free to play but sometimes come with a season pass (that is optional )or the developer just hopes you buy some cosmetics while playing.