From a UK point of view Roku hardware, and Amazon Tv hardware is the equivalent to the Freeview ( digital TV converter) boxes , after a while all TVs had digital TV built in, and the available freeview ( digital TV converter) boxes available /being sold dried up.
Roku hardware ( as well as the likes fo Fire TV etc) provides so called Smart TV functionality to TVs that lack it, now, and for some time virtualy all TVs sold have had smart TV functionality, (in the UK no Roku powered Smart TVs exist ) So why would you need an additional piece of hardware, at additional cost to replicate something that the TV can already do?
The only use going forward for add on "smart TV" devices will be when the inevitable " this app is no longer supported on this TV" messages start to appear, and in order to get BBC iPlayer etc back you will need a fire tv/Roku device