Because prior to the fall of the Soviet Union, Estonia was a part of the USSR. Soviet tactics had been to populate the Baltic States with...ethnic Russians. Hence, 25% of the population are Russian and likewise, the ruling class. You want to get on pre 1991? You go to a Naval School...in Russia (as did Captain Andresson). Thus when the Soviet Union fell, the native Estonians - who naturally fostered a lot of resentment towards their oppressors - couldn't wait to kick them out and to clip their wings. However, much of the Estonian ruling classes were still loyal towards their old masters, especially the military. And they hadn't forgotten how Sweden had shipped them back to their deaths whilst seeking desperate refuge from an angry vengeful Red mob post WWII.
The Estonian head of defense Hermann Simm, turned out to be a Russian spy selling secrets to the Russians and jailed for high treason in 1996. JAIC star witness, Silver Linde was jailed in Finland for drug smuggling. When Sweden smuggled Former Soviet Union materiel and space progs out of Estonia on a passenger ferry, given most of the crew were Estonian, of course, someone was watching and reporting back to the old stalinists.