Eritrea's a dictatorship, it's ruler seems politically shrewd, and it's been under a sanctions war by the US for some time. The sanctions war is not only against Eritrea's armed forces and politicians, but also the country's import/export company responsible for procuring foodstuffs and medicine. The situation has been going on long enough that the only lull in the sanctions was under Trump, and Biden was quick to re-start them.
Even outright american propaganda outlets seem to agree that Trump's removal of the sanctions weakened the government's 'anti american rethoric' amongst Eritreans. Which makes sense. If the Americans aren't at war with you then maybe you don't need the current government. Naturally restarting the sanctions war only re-started the clock.
For those reasons they seem free to fully align with Russia, and the russians seem keen on signing partnerships with them. Syria 2, bogaloo.