Not sure what game you're talking about, but we're talking about 5e here.

a wizard doesn't even really need intelligence if they want to go melee

That makes a wizard that's better at melee than an optimal wizard, not a wizard that's better at melee than a fighter.

strength wizards are surprisingly effective

No they're not.

• They can't wear armor and are limited to a small selection of simple weapons. If they want to use decent melee equipment, they need to burn feats.

• They only get one melee attack per action.

• They're lacking in hit points.

• Their armor class is always going to be inferior to a fighter unless they throw feats into it. Even with 18 dexterity, a mage can only reach 17 AC using mage armor, which a fighter can beat with studded leather and a shield.

and more powerful than fighters until they run out of spells

If you dump intelligence for strength, like you're suggesting, then your spells are going to have low save DCs and your chance of landing hits with spell attacks is going to be pathetic, too.

by then all of the best fighters run out of their resources as well and they're baseline is pretty much the same

Fighters can attack multiple times, have more hit points, can wield stronger weapons, and usually have better armor class, so even if you strip all of their spell slots and renewable resources, a fighter is still significantly better at melee combat than a wizard with the same strength.