Part of the appeal of the BOW was their disposability and deniability. Need a target killed? Send in a tyrant or a team of hunters and once the target is down, they self destruct into untraceable organic goo.
The thing is, Umbrella succeeded, the T-103 was perfect in every fashion. But the falling out between Umbrella America and Umbrella Europe then the downfall of the company meant no more would be produce besides the prototype. If they had just cooperated more, or indeed the power players behind Umbrella had actually been serious about revolutionizing BOWs, the Tyrant project would have been a legit success.