During the suspension period there will be a one line explanation that the user is suspended, with a reason (such as "voting irregularities"), which will be different depending on the suspension circumstances. That is all that is available to most users.
If you are a moderator, you can find out the reason by going to the moderator annotations page for the user.
The general notice is not more details because the details should not matter to others. Suspensions are mostly a last resort, after a user has been warned about their behavior a few times (warnings can be automatic - such as telling a user they might get question banned, or that their reviews have been bad).
There is no reason to embarrass someone by divulging details about their wrongdoing - it is a private matter between themselves and the moderators. Doing so serves nothing but the curiosity of others.