It was signed by Belarus, Kazakhstan, Ukraine, Russia, the USA, and the UK. And signed in a country that only joined the EU a decade later.
As soon as the reality of what the EU was willing to put on the table was crystallised in black and white it became obvious that there was no way on earth that this would fly. This precipitated the unwinding of the Ukrainian polity and the unholy mess that they have to deal with now. The EU has been singularly absent from attempting to resolve or manage this situation because they have no way to deal with the Russians, and the Russians know it.
The Budapest Memorandum does, in fact, have a lot to do with the EU because it has a border with The Ukraine.
At some point in the near future it is going to become really, really, really obvious that the EU in general and Germany in particular is underspending on defence by ~4% of GDP per annum, and has been for 20 years. The bill for this, when the Russians present it (possibly by driving tanks into places where Russian tanks should not be driven) will be much larger than 40% of GDP. Note also, this is not the only massively problematic military border that the EU has; the Mediterranean, Balkans and Aegean are all available for geopolitical lunacy on demand in the near future.
Blame the UK or the USA for not holding Russia to the agreement, if you like, but blaming the EU makes a bit less sense than blaming the OSCE.
And what a mess.