Terrain dictates tactics. If your combats occur on flat open areas (as a DM I knew used to do), then there are no tactics, only a brawl. Corridors (man-made or natural), water, broken ground, higher ground, cover, etc. can all be used by the DM to give options to the combatants.
Sometimes players aren't interested in tactics. I've found the Dodge Action to be heavily underutilized, because players HATE losing attacks, even if the attack has little chance of success or the Dodge would effect many enemies. I've known melee characters who don't carry ranged weapons, because the player just want to run up and smash things. You can't make players care.
Interestingly, the best tactics are often decried as non-dynamic combats. A party of 6, with 2 tanks (sword & board) followed by 2 polearm wielders, followed by 2 spellcasters/archers is a powerful team in most adventures. In the standard 10' corridor, everyone is effective, and they can use very little resources if the Tanks use Dodge. In larger areas, the spellcasters/archers either move to the center or fall back, while the polearm guys move to the sides/flanks. Area effects (breath weapons and spells) are a problem, but they can be mitigated with Counterspell and altering tactics against those enemies.
I wouldn't allow the polearm and archery attacks through the front line in a 10' corridor, but what you should use are hirelings who can protect the mage and form lines in any direction. The more people you have, the more you can cover certain positions.