The first forefather of mankind, Adam, and the first foremother, Eve, stayed in Paradise till they became aware of sex. They became aware of sex through their disobedience of a Divine Instruction to them. They were banished to this earth as a punishment for that disobedience. They and their progeny, mankind, were instructed to follow the divine instructions that would come to them from time to time to gain their entry into everlasting Paradise. And, if they disobeyed, they would suffer everlastingly in Hell!
Sex now, in this world, is how life, although short and uncertain, is propagated and spread. It has thus been given some sanctity, but its unrestricted use spells the undesirable spectre of strife and stress in society. It must be restricted within the bounds of marriage. Sex outside these bounds is, for mankind, like the forbidden tree for Adam and Eve while in Jannah.
And I do not think there is any place for sex in Jannah! There is no need for it there.