several t2.micro better than a single t2.small or t2.medium

I read EC2's docs: instance types, pricing, FAQ, burstable performance and also this about CPU credits. I even asked the following AWS support and the answer wasn't clear.

The thing is, according to the docs (although not too clear) and AWS support, all 3 instance types have the same performance while bursting, it's 100% usage of a certain type of CPU core.

So this is my thought process. Assuming t2.micro's RAM is enough and that the software can scale horizontally. Having 2 t2.micro has the same cost as 1 t2.small, assuming the load distributed equally between them (probably via AWS LB) they will use the same amount of total CPU and consume the same amount of CPU credits. If they were to fall back to baseline performance, it would be the same.

BUT, while they are bursting, 2 t2.micro can achieve x2 the performance of a t2.small (again, for the same cost). Same concept applies to t2.medium. Also using smaller instances allows for tigther auto (or manual) scaling which allows one to save money.

So my question is, given RAM and horizontal scale is not a problem, why would one use other than t2.micro.