Nitpicking, but I'm not sure that it was ads that killed dash sat navs. At least in my experience, they never really developed to that point where car companies would put ads in.
It was more that they were expensive options to install, a pain to keep updated, and generally weren't all that good.
Even before the live traffic and automatic detour features, phones didn't cost money to keep the onboard maps up to date, and you already had one, so you didn't need to either buy an add-on, or get a special unit for it.
With android CarPlay and Apple Auto, you could just put your phone map on the screen, which was basically the same thing, but a cheaper equivalent, since the hardware was on your phone instead.
I'm absolutely certain that it wasn't ads that put a firm like TomTom on a downward slope. This was actually the first time that I've heard someone proclaim that ads are the reason.
If your business is to sell maps + navigation devices for money and then the times change and now nearly everyone already owns a smartphone with built in gps + some car manufacturers provide sat nav as a default + another company is giving access to a map away for free, well then your business is in trouble.
I've never even heard of ads in TomTom or Garmin, since I stopped using a dedicated sat nav once I had a smartphone, but it wouldn't surprise me if it was one of the things they tried to stay afloat after smartphones became ubiquitous.
So I was around during this time and yes ads did play a part in this, but not like you think. The ads where how these companies planned to pay for the sat nav data (came on a DVD). They had restaurant and gas station suggestion with the same detour "feature".
Fun part is that it fell apart quick since almost no one updated there sat nav and you can still get a 2008 acura with recommendations for places long long gone. Its also fun to see people talking about Zagat rated places on forums from the time.