The reason for Russia's 2022 invasion of Ukraine is supposedly their attempt to prevent Ukraine joining NATO. At least, this was what Putin was asking for assurances about in the weeks/months leading up to the invasion.
But the Baltic states border Russia as well. Furthermore, they isolate Russia from its own enclave, Kaliningrad. They're also well-positioned geographically, being near the Baltic sea.
Why were Russia not equally aggressive prior to these countries (Latvia, Estonia, and also Lithuania) joining NATO?