[Kurona]

I think a big factor is that its toyline has very consistently been very successful since around the mid-2000s, and as such they can rely on those big hits to make a lot of money -- I'm not just talking popular ones like Den-O, W, Kuuga, Faiz; any recent toyline will have been a big hit with kids and hence going back only so far as 5 years is sure to both make a profit, and be far more recognisable to your target audience than V3 or Super-1. In comparison, Sentai is a bit more in-and-out on whether its recent series will be popular (and you can be very sure that Gokaiger and Dekaranger get a bunch of recognition), and Ultraman has seen steady success with New Gen but few that's overwhelmingly so, and having started in 2013 it's taken a bit for it to really build up to the point they can rely on those recent guys.

I'd also argue that none of the Showa Riders were big hits outside of the original and Black, both of which do get prominent marketing and recognition (if not as much). Ultraman has both OG Ultraman and Ultraseven as big pop culture icons, while Sentai only actually focuses on Goranger when looking back.

It's certainly a bit fascinating coming into Toku and seeing this I gotta say. You look at western franchises and it's like... G1 is 90% of Transformers' current output; you get a new MMPR Green toy every two minutes; constant countless reboots and reimaginings of 80s movies. Literally today we just heard about a new Buzz Lightyear movie. But Toku while relying on the same franchises is very happy to keep chugging forward with new additions