I think it’s as simple as calories in vs calories out.
Just riding more doesn’t always mean loosing weight. I ride a fair amount and average somewhere between 10-15hrs most weeks. The more I ride the more hungry I get and therefore I eat more. My weight has pretty much stayed at 75kg for as long as I can remember now.
If I haven’t ridden for a period of time due to sickness / injury etc my appetite reduces and I still maintain my 75kg.
If I want to loose weight I need to accept that I’ll probably be hungry some of the time.
I think there’s a fine line when it comes to the ideal weight. Generally you’ll be less powerful if you’re skinny but all that power isn’t needed to get you up those hills at the same pace when compared to a heavier / more powerful person.
I guess this is where w/kg is a useful metric if you have a power meter. If you’re w/kg is increasing and you’re still healthy then you’re on track. If you’re loosing weight but your w/kg isn’t increasing or you’re feeling unhealthy then you’ve probably gone too far.