because copy right laws in north america are a corrupt. if NoA wouldn’t of kept the trademark claim up to date, i could of came in and grabbed it for myself. i could than create a piece of software titled Mario and Luigi without any connection to the plumbers at all.
Copyright was never designed to prevent that sort of thing, and is not done that way anywhere (or at least anywhere with a notable production of IP).
Copyright is for specific works and certain sub elements thereof. Theoretically they expire but for the US then as it is a new year we do get some new ones, this year is the turn of 1924 --
https://web.law.duke.edu/cspd/publicdomainday/2020/
Trademarks are for general concepts, and need to be narrowed down to categories. They are designed to prevent confusion for your brand in the eyes of the general public or your main customers by avoiding having products named the same thing. The do expire being you can renew them, and do have to defend them (see what is said when most fan games get smacked down, and also stuff like the let's play video agreements that companies put out there).
Patents are for items, and if you live in a backwater like the US and Japan then some aspects of software and DNA sequences too (the rest of the world says software is maths and you can't patent maths) and possibly ways of doing business. We tend to see this less in games but the hardware is a thing -- I think we are now free of NES dpad patents (though controllers are commonly a source for this sort of thing), and software wise I don't know what I have seen lately and probably will have to go back to sega's smooth camera transition for anything anybody got upset over
https://gamnesia.nintendoenthusiast...-and-sony-over-certain-camera-features-in-th/
There are further options (service marks, design rights, registered designs) and distinctions in certain fields but enough of that for now and they vary between places and don't tend to come up -- some of the things with design in the name occasionally specify colours for certain items so can make some trouble at times if someone tries to match the colours.
As for why then while I would not like to face off against Nintendo with them owning both the Mario and Luigi franchise (see also Bethesda vs Mojang with "scrolls"
https://www.theverge.com/2012/3/10/2860164/mojang-bethesda-scrolls-trademark-dispute , or more recently Bethesda and redfall
https://www.pcgamer.com/uk/a-sci-fi-author-is-disputing-a-possible-elder-scrolls-trademark/ *) is a specific work somewhat distinct from the platformers, and this sort of thing often includes a logo or phrase as well. It is fairly cheap to do, nobody is likely to object to it, it might help your accountant at some level (while said trademarks are often valued at $5 or something silly that is a different discussion) and it covers your arse.
*speculation being here that it could be an Elder Scrolls 6 subtitle, though it is also a fairly key aspect of the franchise so it might just be basics (I will have to do some research but I would bet a substantial sum that when pokemon was first rising that while Nintendo probably did not have every pokemon trademarked that pikachu was fully locked down, same idea for that).