I'm not sure what Russia had to gain from violating our (Finland) airspace with military aircraft countless of times before we joined NATO. Yet they kept doing it.

Russia is an imperialistic state that really doesn't like having neighbours that are not under its political and military control. Violating airspace, GPS jamming, cutting undersea cables is just their way of showing force, and damaging us, who they perceive as their enemies for not submitting to their rule.