Leave-on treatment.

Sometimes I find it hard to wait for the treatment time, so I tried purchasing a treatment that I can apply after showering and leave on.

It is a spray type that produces a whipped cream-like foam when sprayed. I applied it to towel-dried wet hair and blow-dried it, and it made my hair soft and shiny, which I think is great.

However, here is one question that comes to mind...

Both leave-on treatments and rinse-out treatments contain similar ingredients necessary for hair, such as protein and keratin, so why are there so many inconvenient rinse-out treatments?

If it contains ingredients good for hair, I simply think it would be better to just apply it and leave it on rather than washing it off.

Just like how we apply skis, lotion, and cream and don't wash them off.

Is there anyone who can answer this question?