I also assume they would use as much code as possible/reasonable for adding SMP, so changing the tick rate would be a lot of work - 20 ticks also simply seems to work out for the Minecraft type of game. Why would one use less ticks? Probably one would not, simply. Why use more ticks? Probably to decrease latency further, but what would 40 ticks lead to... you would have much stuff executing not every tick, but probably process some events more often (could do the same with twice per tick checking), less chunks processed per tick... Also there are other side conditions, like how many packets per second should the player send? 40 Moving packets per player would be harder to keep up to considering the networking processing, so 20 could even be the optimum for it all. Redstone updates how often... It's an eco-system built around the somehow working 20 TPS, probably there is no simple answer (other than it was so from the start and it worked out).