The general idea is that every Device can communicate with every other Device. Bluetooth was added to everything in hopes that we could better automate every aspect of our lives when a critical mass of devices can talk to each other. The Bluetooth receiver in your alarm clock tells your coffee machine to start remotely. But we quickly realized that the overhead isn't worth the payoff. But up until that point we made Bluetooth glasses, beanies, dash buttons, replaced inafred in most devices, power tools and appliances. It wasn't that bad, but there were moments when you would pick up a smart nose trimmer and wonder why they included it.
And in the mid 2010s it got worse where everyone and their mother put bluetooth in anything and everything. IoT became accessible, only to be used in the dumbest way to try and get rich from Kickstarter.
only to be used in the dumbest way to try and get rich from Kickstarter
Followed of course by an obligatory Shark Tank appearance asking $2 million for 4% of their product where all profits go to the Zuck (the cost per customer acquisition is the entire margin and its all spent through facebook and ig ads)
It wasn't so much that it was put in stuff that wasn't useful it was more that it was put in stuff that needed something better than Bluetooth but they put in Bluetooth because it was new and shiny rather than old boring radio.
The problem with Bluetooth, especially back then, was that the range was terrible (about 1 ft in my experience), you couldn't connect to more than one thing at a time, it consumed quite a lot more power than radio (we have ultra low power modes now), and the bandwidth wasn't great either (still somewhat the case but the bandwidth has improved). So you had things like Bluetooth car keys which were like keyless entry systems we have today, but rather than using radio they used Bluetooth so half the time you'd go near your car and nothing would happen.
A lot of the cases where things used to have Bluetooth now use Wi-Fi today. Of course there were always things that had Bluetooth for a gimmick, but the vast majority of it was simply things that had Bluetooth when something else would have been the better option. Back then Bluetooth headphones were seen as a gimmick because they basically didn't work, now they work, so they're not a gimmick anymore. The perception of if something is or is not a gimmick is more about if it works rather than if it actually is a useful product.
Radio in this case meaning an analog signal. Just fire the appropriate good vibes energy at the car rather than trying to send some packets over a wireless network. It didn't work mostly due to the lack of any kind of redundancy. If a packet got dropped then it just dropped, it was gone.
When we started adding some decent protocols to Bluetooth it became more reliable, but it's still not great range because of the frequencies used. Of course these days you would use Wi-Fi not analog radio, to get all of the advantages of Bluetooth but a much greater range and reliability.