I think valve can earn more money if they release battlepass sooner.

dota has 3 types of battle pass buyers:

1. big whales: they gonna buy 1k+ levels in day 1 and they don't care how much battle pass has duration.
2. mid budget players: these kind of players normally buy battle pass level 100 and bundles and aim for arcanas. this players also don't care about battle pass duration.
3. low budget players: these players buy level 1/50 battle pass and maybe 1 bundle. if they can grind close to a big reward for example level 370 arcana maybe they spend more money. for example if they grind to level 300-330 maybe they buy 40-70 levels but if they only grind 200 levels they can't afford to buy 170 levels and they will skip it.

btw in nemestice and aghanim I saw people who after 1 months wanted to buy battle pass but they skipped it bc they didn't had enough time to grind. I am sure if they had more time they definitely would buy battle pass.