I think Soviet people felt Latvia, Estonia, and Lithuania were a sort of the West of the USSR – better services, better retail (it was different in each city and each republic of the USSR), cleaner streets, etc.

Secondly, it was a place of the music festival (of young pop music performers), probably the most famous in the USSR - I can recollect myself as I was a kid at the time (in Soviet Georgia) - Soviet TV was super boring, so people loved the Yurmala music festival. Doubt there would be Russian investments after the USSR collapsed if not this festival that created the glory of Yurmala as well as connections between Moscow money and local beneficiaries.

Yurmala festival, a TV program, 1987:

Watch the first 20 seconds – the TV intro is epic, lol. Soviet AF.