Why no brand does this?

[aguade]

An adaptor so you can use 120, 140 fan holes to mount drives 3,5 or 2,5. My case (Enthoo Luxe) and many others have a huge space at the top which goes unused if you don't have liquid cooling. That space would be wonderful for putting hard drives. I guess an adaptor wouldn't be too difficult to make, just like there are 5,25 to 3,5 and 3,5 to 2,5.

[homeap5]

Because there are two types of pc cases - functional ones with lot of bays for drives and extensions and circus style cases - with lot of space for fans, leds and fireworks. If you want good functionality - choose first option.

[DoctorNick]

Yes would also be great in smaller cases. But for yours Enthoo Luxe. Do you really need more storage? You can fit 6x3,5" or 8x2,5" in the front bay? Or did you remove that for watercooling?

[greenhorn]

Solutions for that do exist, but they are not primarily intended for that use case. Look at 5.25" to 3.5"/2.5" adapters that have fan mounting holes such as this thing (found on the German amazon site) https://www.amazon.de/dp/B0091ETHGO/ref=psdc_1626220031_t2_B07H2C7HXH