In aviation - maintenance engineering and piloting, the existing licencing system is so tailored and thorough as to make university degrees pointless. So, they have no real value.
In other aviation roles (design, research, management, accountancy, quality assurance...) the qualifications for the job are less clearcut, so degrees start to have significant value.
Partly because of this, university engineering degrees are almost entirely tailored to management, design and research jobs - and thus have little or no relevance to maintenance.
It's just how it is.
G