It was mostly about the perception that people with a bachelor's degree had not learned anything useful yet.
There is a lot of variation between countries, but European countries often have a dual-track system in higher education. You can choose between the academic track (universities) and the vocational track, with more people ending up in the vocational track. Some fields are available in the academic track, some in the vocational track, and some in both. Professional fields such as healthcare, business, and engineering are often available in both, with the tracks preparing for different roles in the field (such as nurse vs. doctor).
Imagine being used to an educational system with two kinds of degrees. Some indicate practical studies preparing for a job, while others tell of longer theoretical studies and specialization. Suddenly the system changes and you start seeing a third kind of a degree: shorter theoretical studies without going particularly deep in anything. What use do you have for people like that?
I know plenty of people with “only” engineering bachelors degrees from my Alma Mater who would easily outperform people I’ve met with masters, so the same thing as the masters-holders I suppose?
It's not about being better or outperforming someone. A doctor is not supposed to be a better nurse. Similarly, engineers in the academic track are taught different things and prepared for different roles than engineers in the vocational track.
If you just need an engineer, someone from the vocational track will probably be more productive than an academic engineer due to more relevant education. Assuming a similar level of talent, of course. You only hire an academic engineer if you have an actual need for theoretical education. Or if you have a job where the specifics of the education don't really matter. Or if the academic engineer is from a higher-tier institution and likely more talented, despite the education.
There is a lot of variation between countries, but European countries often have a dual-track system in higher education. You can choose between the academic track (universities) and the vocational track, with more people ending up in the vocational track. Some fields are available in the academic track, some in the vocational track, and some in both. Professional fields such as healthcare, business, and engineering are often available in both, with the tracks preparing for different roles in the field (such as nurse vs. doctor).
Imagine being used to an educational system with two kinds of degrees. Some indicate practical studies preparing for a job, while others tell of longer theoretical studies and specialization. Suddenly the system changes and you start seeing a third kind of a degree: shorter theoretical studies without going particularly deep in anything. What use do you have for people like that?