Lyxen
Great Old One
(bold added) Not directed at @Lyxen.
IME if your DM is only attacking from the front, that isn't very exciting.
I'm not saying that my DM(s) do, I'm not saying that I do it as a DM, I'm just saying that, statistically, when you look at fights, it is what is happening fairly frequently. For example, assuming that the adventurers start the fight 50% of the time, 50% of the time it's what is going to happen.
When I DM, I often attack from multiple directions, so there is really no place for casters to go to be safe since the parties aren't large enough to circle them
Of course, things like that happen, but do they happen every fight ? I don't think so, moreover even if the fights start that way, the martial will position themselves next to the threat to attack it or intercept it.