It's the same slow ass crappy development cycle we have to tolerate on all new devices. 1st generation is slow as hell and we just have to be happy it works at all. Then when just being "Smart" isn't enough they'll start to advertise speed. Then when enough people read various online consumer reviews and gravitate to the faster/better models all of the manufacturers will get them to where they should have been 5 years ago.
Seems like you know why things are what they are! What I would add is these TV divisions are NOT traditional tech companies like an Android phone division. They have year-long cycles with incremental upgrades year to year. Something like Moore's Law is completely off their map, they are closer to appliance sales where little changes over time.
I have two smart TVs myself, but I often recommend people DON'T get them and invest in Rokus instead for that reason. My oldest smart TV came out when the Roku 1 was still king, but unlike the TV's smart guts I can easily upgrade the Roku. For that ST50 I now use the Blu Ray player's smart functions rather than the TVs because the performance was so poor. The ST60, released just a year later, is much better.
What annoys me more than device speed is the fact that some smart devices can't access some streaming services. Almost anything gets Netflix, but if you need say Amazon Prime streaming it's a crapshoot. The other issue is that not all smart devices can easily update their apps for each service, so on some devices even the same service like Netflix has a MUCH MUCH better GUI. That is beyond TVs, the Netflix app on a new Roku is so much better than the one on the AppleTV it isn't funny. I am to the point where I have a lot of smart devices hooked into a smart TV and I my wife has to chose the option that is the best for that service.
The honest truth is all this smart/roku/streaming stuff is a mess, a bunch of different companies going in many directions with few standards. We have gotten spoiled by things like Spotify on the music side, but for video content it looks to remain a mix of walled gardens for a while with varying quality per device. It is part of the reason I don't trust steaming as our primary consumption option, as my mediaserver filled with local content combined with my Kodi clients gives her a top shelf and consistent experience anytime. It is like music in the Winamp days, if you want a great experience you have to make it yourself.
Video companies learned how hard it is to put the horse back in the barn when you go the Spotify route, so they will make it a pain for as long as they can to maximize revenues.
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