I had an Asus TF700 tablet which had HDMI out and a keyboard dock/touchpad probably about 10 years ago.

It could have been a decent concept if the Tegra 3 chipset wasn’t a little underpowered and the onboard storage so slow.

On new stuff, a Bluetoothu keyboard and mouse more or less solve input, and USB-C should solve video out (and input if you want). Modern phones should be powerful enough for basic desktop use, I just don’t think people want it.