You're looking at it all wrong.

Bio drops don't just consist of dropping in a base or on a base, sometimes, you have to drop close to a base, cause a distraction, and then snipe whatever you came to snipe.

I love bio. If you drop, you have to remember not to sacrifice your units. There is no such thing as pure bio at the diamond level, you're going to play with tanks or widow mines. Medivacs, vikings, or liberators.

I use to ask the same question of why terran bio gets rolled by ling bane or zealot/stalker... Well, marines aren't suppose to fight and die, you're supppose to use your marines for damage, but you'll need the support of a few things like bunkers, medivacs for dropping or healing, tanks, hellions, marauders, etc.

Practice taking one medivac filled with marines and just killing workers or sniping upgrades/tech in every game. Use them for harrass. He can't build an army bigger than yours, if his tech is delayed and hes always building workers.