I don't know that this is true.
https://www.numbeo.com/crime/region_rankings.jsp?title=2019-mid®ion=150
Vilnius and Tallinn rank as safer than average for European cities and Kaunas and Riga slightly less safe. It looks pretty comparable to Western European cities.
Regardless, I did not feel unsafe whatsoever while there. Streets were well lit, there were plenty of police, and I didn't notice any homeless or sketchy things on the street. However, I did only stay in the more touristy old town areas. I'm sure there are bad parts of this city, just as there are all cities. Over the next month, I'll be doing weekend trips to Riga, Latvia and to Tallinn, Estonia. I'll report back how they are as well.