Yeah, but they can take any route from the huge collection. Sherman Hill came with TS2013 and TS2016. Then make regional starter packs etc.
Sherman Hill should not be in a route pack again for one simple reason: it is already featured twice, as you stated. Also, the cars in Sherman Hill refuse to stay on the train in the very first scenario, which is also the first actual scenario I've played and I sought advice over as a new player at the time. BTW, the cars have never been fixed. I doubt they will be at this point because of other content using them since. Cajon PAss also had a scenario I've played with those cars (actually from the 24060 pack, I believe) where I actually failed the scenario when some cars fell off in the exact same way without me noticing. Things that are not working correctly should be looked at and fixed with these annual packs, but it seems this is no longer a compelling interest. If they fix the cars and also, as I look at it, fix the scenario timetables, then sure, feature Sherman again.
Why can't we have some new routes and trains? For the UK, let's do North Lincolnshire/East Midlands Nottingham/Doncaster to Cleethorpes with a Class 60 in DB/EWS for freight, Class 170 EMR/Class 185 TPE for passenger. For Germany, The Rubelandbahn from Kassel to Rubelandbahn with the HVLE/OHE BR250 Blue Tiger for freight and the BR285 for passenger. For the US, the GE Tier 4 GEVO for freight (any operator), Amtrak ALC42 with Siemens coaches for passenger. A route in Florida for something new and refreshing.
Another idea would also be to spend a little on the AP Sky Weather Packs, Track pack and Veggie pack, and also use my reshade reset. It'll make your game look more real. You can follow the progress/give feedback on my mod here: https://forums.dovetailgames.com/threads/realistic-reshade-preset.75337/
Replacing my old 10-year-old LED monitor with a more modern one made a lot of difference to the way TSC looks.