Why are my Cacti leaning?

They look healthy and otherwise are prolific growers but have started leaning. Watering only when soil is dried out Currently getting 6 hours direct morning east facing sun and bright shade the rest of the day.

They look healthy and otherwise are prolific growers but have started leaning. Watering only when soil is dried out Currently getting 6 hours direct morning east facing sun and bright shade the rest of the day.