They weren't protesting the tax on tea. The Tea Act essentially (1) exempted the East India Company alone from taxes on tea, giving it an unfair advantage of almost monopolistic strength and (2) undercut local smugglers who had been profiting from the Townshend Acts by illegally importing tea.

It was a protest against an unfair monopoly and what we would call today dumping, not a protest against the tax itself, though the tax was hideously unpopular.