The game was initally released only on PC and the Console Version got added later on. At that point some routes were already in full production without thinking too much of Console Versions for it. The game launched a month ago on Consoles (despite the Founders Edition) and they are porting them over while they still have other routes in full production. Added that DTG isnt a big AAA studio the resources are a bit more limited. In the future, when they start developing a new route, they might are able to develop it from Start to End with PC and Consoles in mind and we might see a release of new Content for all Platforms at the same time. Just my 2 cents of course.
Not all the game was built for PC in the start and saw that people were asking if this would be on the console. It takes a bit for things to work properly on the console before they release it. after the consoles get WSR and then RSN both PC and console should be receiving new DLC at the same time.
I´m pretty sure the Console Version were on their overall TSW roadmap before they started development. They announced a Console Version of TS way back in a ID @ XBox showcase at Gamescom some years ago (I think it was 2013 / 2014). Which then they choose to not port over TS but going with TSW instead. But as for roadmaps they probably hadnt an exact date for that set, surely more early on, but it took some time to get it all working in a state they felt confident to release. And at this time these routes wer all already in production. I do hope that we will see new Routes for all Platforms at the same time or at least within some weeks in the future.
i do hope we see the branch lines added on the paddington to reading route in the next few months/years, instead of just running backwards and forwards to to reading/paddington and back