>I am sure this question has been asked a million times. And yet I am asking it again. I see everywhere online stored procedures named with prefix sp (e.g. sp_custom_account). Is there a technical or a logical reason for that? Since stored procedures are in SQL DB Programmability -> Stored Procedures, why need to tag them as SP still?

There is no particular reason, other than whne looking at the name that you can identify its a stored procedure.
Since we are not a heavy user of stored procedures we do not use any naming convention for stored procedures.