In Jainism, the core ideal is brahmacharya — restraint over sexual desire.

For householders, sex within marriage is traditionally accepted only as a limited concession, mainly for:

• procreation
• maintaining household life
• within fidelity and self-control

It is not seen as a pleasure to be pursued freely.

So, the reason traditional Jain thought allows a married man and woman to have sex is because that fits the classical householder framework of marriage and family life.

For two married men, classical Jain tradition does not recognize that as the normal marital framework. In traditional Jain ethics, marriage is understood as a man-woman household union, so the same permission is not extended in that form.

More importantly, Jainism judges sexual conduct by:

• restraint
• non-attachment
• fidelity
• avoiding harm and excess

So the main point is not simply “married = allowed,” but how much restraint and purity is maintained.

In short:

• Marriage does not make sex fully free in Jainism
• It is only a regulated allowance for householders
• The ideal remains control of desire, not indulgence

If you want, I can also explain this in terms of Jain grhastha dharma and the five anu-vratas.