It is better to ask snarknews about this stuff, but maybe I can try to explain.

Generally, the name of GP coming from local contest in which it was used or group of authors who prepared this contest. Let's take a look at GP of previous year:

GP of Japan was just a compilation of old AtCoder problems used in Petrozavodsk training camp, so it wasn't a local contest, but problems have Japanese origin.

GP of Eurasia and GP of Siberia: There is popular contest for Russian teams called All-Siberian Olympiad. It has online qualification round and onsite round, both are used as OpenCup rounds. Since you cannot use 'GP of Siberia' twice, 'GP of Eurasia' is used. I think that 'GP of Novosibirsk' would be better but whatever.

GP of Spb, GP of Peterhof and GP of Two Capitals: SpbSU hosts three university championships each year, and each of them is used as OpenCup round. Again, you cannot name all of them 'GP of Spb'. Peterhof is where campus of SpbSU is located. 'Two Capitals' are Saint-Petersburg and Moscow (in Russia these two cities are often referred as two capitals), this SpbSU championship was used in local Moscow competition, so it was like one contest in two capitals.

Eastern GP: I think it was some Siberian regional + some Chinese problems to make it harder. Both locations considered East.

Czech GP: Not sure, probably it was some local Czech contest.

GP of Dolgoprudny: Dolgoprudny is small town where MIPT campus is located. This contest was prepared by guys from AIMTech, and there were a lot of MIPT alumni, and the main purpose of preparing this contest was to use it on MIPT workshop.

GP of Europe: it is CEPC, probably the strongest Europe regional (maybe except for NEERC).

GP of Gomel: prepared by tourist

GP of Moscow Workshops: I think that it was PR of Moscow Workshops (all previous GP named with some place), but the contest is prepared mostly by Endagorion (who is one of the guys behind Moscow Morkshops) and MIPT Jinotega

All other GP are named after group of authors who prepared the contest.

General idea why Russian locations are precise and others are vague like 'Europe' — because most of contests are Russian so you need to somehow distinguish between them.