I figure they don't dodge melee attacks as much simply because they are using the time you're hitting them to attempt to hit you. That's just like when you get hit, naturally you should take a swing at the enemy during that brief invulnerability you have. So while you lay on the combo, its just waiting for you to stop for just a second to hurt you.

But at a distance it cannot do that, so it dodges because there's no way it can counterattack (well some enemies have distance attacks but I'm just going off of the basis).

Plus...it'd make the game slower if they did dodge melee attacks more often...

In the higher Tiers, you will see more evasion from enemies. It's progression.

i.e. :
In Tier 1, Wolvers hardly evade, maybe on occasion. They do not evade any bullets. They only move swiftly when they are planning to attack you, if I recall.

In Tier 2, Wolvers will usually flank to your backside. They will evade bullets, sans Alchemers.

In Tier 3, Wolvers will near-constantly, completely teleport, flanking to your backside. They will always evade bullets, sans Alchemers. This also makes dealing with them a pain if you're using a heavy sword.
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Other enemies, such as Gremlins, gain shields in Tier 3, and all Gremlins will feign at your bullets. They somewhat strafe out of the way when doing so.

I found bombs to be fantastic against wolvers. Far better than trying to shoot them or getting bitten from melee.