Personally, my waning interest in IoT devices is due mostly to lack of increased utility. A new fridge that displays my Google Calendar doesn't really offer me much additional value, at the cost of adding another failure mode to the device. Having had several newer appliances with failed touch-pads or electronic modules, I'm loath to buy a device that has even more fancy electronics.
As for phones and tablets, I feel like I've reached the point where new iterations don't offer much additional value. Roughly equivalent to how I felt about PCs/laptops 7-8 years ago. Battery life isn't getting better (without going large), screen resolutions are great, cameras are great, and the devices are fast enough for the apps I use most (email, calendar, phone, camera, Flickr, and Kindle).