My one experience with FORTRAN was when working for a big dutch architect who made spaceframes, I built their cad system and a colleague built the finite element analysis module based on an existing library. We agreed on a common format and happily exchanged files with coordinates, wall thicknesses and information about the materials the structure was made out of and forces in one direction and a file with displacements in the other. It worked like a charm (combined C and FORTRAN). I thought it was quite readable, it felt a bit archaic but on the whole not more archaic than COBOL which I had also worked with.
The reason that library existed in FORTRAN was that it had a native 'vector' type and allowed for decent optimization on the proper hardware (ie: multiply and accumulate) which we did not have. But the library had been validated and was approved for civil engineering purposes, porting it over would have been a ton of work and would not have served any purpose, besides it would have required recertification.
As for VAXen: A VAX 11/780 is a 32 bit minicomputer, something the size of a large fridge (though later there were also smaller ones and today you could probably stick one on a business card). It had a - for the time - a relatively large amount of memory, and was a timesharing system, in other words, multiple people used the same computer via terminals.
They weren't special per se other than that a whole raft of programmers from those days cut their teeth on them either because they came across them in universities or because they worked with them professionally. They were 'affordable' in the sense that you did not need to be a multinational or a bank in order to buy one, think a few hundred thousand $ (which was still quite a fortune back then).
I had occasional access to one through the uni account of a friend, but never did any serious work with them. The first powerful machine I got my hands on was the Atari ST, which had a 68K chip in it and allowed the connection of a hard drive. Together those two things really boosted my capabilities, suddenly I had access to a whole 512K of RAM (later 1M) and some serious compute. Compared to a time shared VAX it was much better, though the VAX had more raw power.
Concurrent to that I programmed on mainframes for a bank for about a year or so, as well as on the BBC Micro computer (6502 based) and the Dragon 32 (a UK based Color Computer clone).
Fun times. Computing back then was both more and less accessible than it is today. More because the machines were so much simpler, less because you didn't have the internet at your disposal to look stuff up.