Russian citizens in Estonia aren’t permanent residents, they have mostly been living there for decades, however, due to the fact that Estonia did not grant them citizenship automatically upon the dissolution of the USSR, they’ve been unable to obtain it. Many of them keep Russian citizenship for practicality. Obtaining Estonian citizenship is hard, revoking Russian citizenship is even harder, and there are benefits to holding Russian citizenship. They can visit friends and relatives easily and can work in Russia with less difficulty. Many Russian citizens have also grown up their entire lives in Russian-speaking communities. Most of them are part of an older generation and have been unable to acquire the proper proficiency in the Estonian language to complete the citizenship test. It also doesn’t help that communities with Russian citizens tend to be kind of isolated and disenfranchised, so it’s kind of punching down IMO.