The excitement of doing something 'forbidden'.

It's fairly uncommon and therefore exciting.

It's tighter than vaginal intercourse.

The anal muscles are stronger and more controllable than vaginal, so the sensation changes more.

For the flattering view of the partner.

The giver feels dominant.

I don't agree that most men find it pleasurable.

The excitement of doing something 'forbidden'.

It's fairly uncommon and therefore exciting.

It's tighter than vaginal intercourse.

The anal muscles are stronger and more controllable than vaginal, so the sensation changes more.

For the flattering view of the partner.

The giver feels dominant.

I don't agree that most men find it pleasurable.