In my opinion, the popularity of a UNIX platform is tightly tied to
the availability of the platform at university.
If DG was available to tinker on, to run ROFF, to write small programs
for other reasons, to introspect and familiarise yourself with, Then
for those students, it became the logical choice.
If they ignored the tertiary education market, sold into industry,
they could have established a huge loyal fanbase in E.G. Finance and
Insurance. Or in the decision support systems in Oil. Or shoe makers
inventory control. But if you don't have a cohort of students who
recognize your brand, your flavour of UNIX, and you then face these
students flexing muscles at purchase time, Instead of "lets buy the
upgrade option from DG" you get "why don't we buy Sun, and then get
cheap kids to run it"
TL;DR DG did not have significant presence in the tertiary education
systems I played in (York, Leeds, UCL, UQ) and by my visibility,
almost any tertiary education facility I have seen. They didn't feed
the beast.