The 797 had been in decline for years - you've got it a little wrong - Uno originally took it over and ran it as the 797 for a few months as this post on another thread shows
https://www.railforums.co.uk/threads/arriva-buses-including-greenline.195210/page-42#post-5973980
I thought the 712 was Arriva's attempt to run a St Albans - London service, but again it didn't last long. And the replacement for the 797 was the 614 which only went as far as Queensbury - where the 797 continued into Central London ?
Setting aside the "disruption" occasions, I'm not sure there has ever been much demand for travel from Stevenage - St Albans. In fact AIUI, if you go back to the early 1980s there wasn't even a direct bus between St Albans and Steveange - that only changed when London Country re-cast some Green Line services in the early 1980s and replaced the Hitchin - London Victoria 732 with the Hitchin - Heathrow (and Reading at one point) 733.
The 733 wasn't overly successful and wasn't registered as commercial by London Country, but Herts County Council made it a contract which was run initally by Armchair of Brentford and then later having been truncated to Watford, by Luton & District.
The current "group" of services which linked Stevenage with St Albans came into being in the late 1980s when London Country recast the 300/303 Hitchin - Potters Bar and 340/341 Welwyn GC - Hatfield - St Albans - Hemel Hempstead routes. The 300/303 were diverted at Hatfield to then head onto St Albans and Hemel replacing the 340/341 - obviously there have been some changes since then, but the basic pattern remains. The Hatfield - Potters Bar section became a Herts County Council contract route. So the fact there is a Stevange - St Albans - Hemel route only came into being out of operational convenience - not really as a result of passenger demand.