It also buys them into Airbus as customers & supporters, aligns commercial, technological & employment interests across European nations in numerous ways. If Airbus didn't already exist, they'd rationally want to create it rather than just leaving the market to the US and China. I'm sure the four million parts and 30 countries aspect adds a lot of complexity and bureaucracy, however it might be a reasonable price to pay for the benefits they derive natively in Europe from having an Airbus (as opposed to not) and so many nations being part of it.

Government employment is not necessarily beneficial. It's not governed by economics.

You can have completely useless roles exist for hundreds of years.

Skilled or unskilled labor is better in the private sector for everyone's sake.