Right, not the only reason, but it's a sticking point.

You shouldn't need to connect to your smart thermostat by using the company's servers as an intermediary. That makes the whole thing slower, less reliable, and a point for the company to sell your personal data (that last one being the ultimate reason why it's done this way).

Everyone having a static IP is a privacy nightmare.

There's a reason the recommendation in the standard for ipv6 had to be amended (it whatever the mechanic was) so that generated local suffixes aren't static. Before that, we were essentially globally identifiable because just the second half of your v6 address was static.

Which is why IPv6 was created. Everything used to get a public routable IP. Large company’s such as ATT and IBM got a whole /8 to themselves. NAT made it so we did not run out of IP’s in the 2000’s