why do different online casinos have completely different blackjack rules

Was trying to set up a blackjack spreadsheet and realized that every online casino I checked had their own version of the rules. Some allow double down on any two cards, others only on 10 or 11. Then you got the ones that let you resplit aces, or not, or only let you split once. Deck counts jump around too, and a few places had the dealer hitting soft 17. Got me wondering if there’s any real method to this madness or if they’re just doing it to keep advantage players on their toes.

For anyone else jumping between sites, do you just memorize the basic strat for each rule set or go with your gut and hope for the best? I keep catching myself defaulting to the “book” moves, but then realize I’m playing with house rules stacked deeper than the original game. Starting to feel like the casinos are banking on us not noticing the small rule tweaks that jack up the house edge. Curious what approach has worked for folks here who keep bouncing to find the best value table.