It really does astound me that Fourze's ratings are so low, given merchandise sales.

Are there any easy to overlook factors that might be contributing to this?

Really? Crap.

Well, to be fair, this is the Sentai after Gokaiger. My guess is that some people still like Gokaiger more than the current Sentai that's airing.

Well there's that, and the fact that Go-Buster is pretty boring/underwhelming/bad compared to nearly any show. I hate to be so blunt about it but it really is just so average and bland that it's hard to push through.

I wonder why Fourze's ratings are so low. I mean sure it's no Ryuki but being around Decade's level? Wow.

Go-Busters has been rather bland and uninteresting so hearing that their're the lowest ranked Super Sentai of all time doesn't surprise me in the least.