I think the observed feminisation isn't a causal factor, but instead shares a causal factor - that every space must now accept everyone. This causes a few problems.

0. One of the ideas that has tagged along with inclusion has been changing from an input focus ("e.g. No girls allowed in treehouse!") to an output focus (Fewer girls than boys are in the treehouse). In the input focused model, you want to change the rule to stop excluding girls. In the output focused model you also need to change the treehouse to be more attractive to girls. From this, any 'deviant' interests that happen to be gendered (or racial, cultural, etc) get suppressed in the name of creating inclusive outcomes.

1. Most humans have a natural urge to conform to those around us, some just experience it stronger or weaker than others. When 'deviants' are included in a non-deviant space, their deviant tendencies face a subtle yet strong conformity pressure that wouldn't be felt if they were excluded entirely.

2. 'Deviants' being accepted more widely means they don't need to create or find their own spaces. Hence there are fewer spaces where the deviation is locally normal, which would allow the conformist pressure to enhance and refine the deviation.