This has nothing to do with religion, and everything to do with not having the population collapse, because we've become so focused on pleasure that we forgot why there is a biological advantage to it being pleasureful... to do it more and reproduce more. But modern technology has eliminated that pesky side effect of children.
The pleasure can and does still exist. It's not like it gets removed when sex is ends in a pregnancy. It doesn't have to be some mechanical act, the way you seem to be framing it.
I get the sense that by pleasure you’re referring simply to orgasm during sex itself? Again, that is part of the problem. As for religion, I believe your view is in fact rooted in religion which strategically and historically segmented the sexual experience; not that you’re explicitly espousing a religious view but that it is implicit in what you’re suggesting.
You’ve used the word “great” and “pleasure”, however you’re not specific about what you’re talking about. I’m having to guess at what you mean, and you keep telling me I’m guessing wrong, without clarifying your point. This isn’t productive.
The pleasure can and does still exist. It's not like it gets removed when sex is ends in a pregnancy. It doesn't have to be some mechanical act, the way you seem to be framing it.