Some of it was to make it easier to talk for people who didn't know the language of the country on the map, I heard that polish military maps of the UK apparently were "localized" the same way - and the persistent rumour is that under "take all of europe in counterstrike to prevent USA supplying the invasion" plan, Polish forces were to occupy major portions of UK.
Imagine trying to figure out how to correctly say "Port Hueneme" if you're a random Soviet officer. Probably best they were phoneticized if only so other Soviets would have some idea of what you were talking about.
Also, I think we can feel somewhat confident that over the years the Soviets intended for special operations to take place on American soil. Few non-nuclear things screw with preparations for a deployment overseas more than transmission power lines for San Diego and/or Norfolk dropping, or an outbreak of a crop disease, or what have you. If you're feeling sporty, assassinate a few people (preferably false flag ops to stoke domestic divisions).
Interesting to see the place names phoneticised to Cyrillic. Not sure how useful that would have been in an invasion.