It was a Tatsu park on the Alpha Workshop (no idea how you got it from that to the main game, by the way), not a Sky Tower blueprint. The Tower wasn't made to be copied into other people's parks in the same way individual building blueprints are.
There were numerous methods to retain work from the Alpha 1,2,3 -> Beta -> Release
It was not that difficult. I have a bunch of my Alpha 1 work blueprinted for future use. Most of it does not work quite right now or needs to be updated since so much has changed, like rooftop corners got changed a lot.
Anyway, if you share a park, then anyone that downloads it can select objects from it and blueprint them. That is by design.
I'm just not going to bother uploading to the Workshop in future -.-
Either way, a simple PM to me wouldn't have been hard. I'm rather protective of my work since I put a lot of time into it ( the Sky Tower took at least 30 minutes because of the octagonal top). I uploaded Tatsu to be looked at, not used.
YOU uploaded something to the workshop. YOU installed Steam and Planet Coaster. YOU accepted the EULA's...
Now, let's be honest. At the end of the day... If Frontier themselves decided to use your "creation", without crediting you, and you were not happy about it, any arguments you have would simply be nullified by the fact that your "creation" is a derivative work of Planet Coaster's assets, which they own. In the same way that anyone else using something downloaded from the Steam Workshop can. This is like Andrew Lloyd Webber VS. Roger Waters territory...
Even if there was some option created where you could tick your parks uploaded to the workshop to not be savable: based on how Planet Coaster/Steam Workshop works right now, it could be easily circumvented without a tremendous amount of development effort. That's just basic computers: If I have your 'physical' data file then I can manipulate it.
Nobody owes you anything.
If you only want people to look at your stuff, then the workshop is simply not for you...
Upload it to YouTube and post it in these forums! We'd be happy to see it!