The lack of marketing suggests one of 2 things to me:
1. Sub-Terra isn't actually reopening (at least any time soon). Clearly work is going on but that could be for a planned use of the space later on in the season that is just more convenient to setup now.
2. The ride does reopen but is almost identical to how it closed. The length of time it has been closed for is unusual. For an enthusiast 8 years is a very long time. But for some visitors that might of, for example, stopped visiting when they started a family in the early 2010s and now have kids that are old enough to visit themselves, might be visiting without even realising the attraction had closed. I myself last visited in 2014 when Sub-Terra was still open. If the rides going to reopen without changes (and in a year in which another classic attraction is having major changes) it might weaken their marketing strategy to be seen advertising 2 old rides, like they have nothing new.