I think a more charitable interpretation of Elastic's motives in the re-licensing would be to view them the same as your motives for your side project -- allow

I think a more charitable interpretation of Elastic's motives in the re-licensing would be to view them the same as your motives for your side project -- allow free use to anyone except those wanting to offer it as a hosted service. You say that you've licensed your side project with MIT and Apache2 but with an exclusion. In other words, it's neither MIT nor Apache2 and it's unclear how your exclusion would hold up legally (hopefully well!). At Elastic's scale, uncertainty over a license is too risky, so I'm sure they paid their lawyers $$$ to ensure that the SSPL would hold up in the scenarios that were important to them.