While some car manufacturers have claimed interference as the reason for not including it, the plain and simple truth is that very few consumers, especially those under 40 or even 50 years of age, are using or requesting AM radio.
The very few cases of "no AM at all" are particularly strong with smaller European manufacturers such as Volvo, a brand that comes from a no-FM-at-all nation and which has limited world-wide sales. But in most cases, the lack of AM is limited to specific electric models only. And Tesla. Still, it's a tiny percentage and, likely, the focus in Congress on this will make sure that it is very limited.
If it wasn't included in the dash, the simple truth is that few would miss it at all. Second, there are many ways to receive alerts other than AM radio. FM stations also carry alerts as do TV stations, cable systems, and cell phone service providers.
TV and FM are line of site. There are lots of areas where you need extra antennas to get TV and where FM is marginal or not available.
n fact, cell phones, at least where I live, get more alerts than are broadcast over AM radio. Amber alerts (child abductions and be on the lookout (BOLO) messages) are blasted out to cell phones; Blue alerts which indicate a law enforcement officer has been killed, injured or is missing at times with a suspect at large are also sent to cell phones here (users have the option of disabling amber and blue alerts if they wish).
I don't know a single person where I live who has not disabled that function. Our area is a smallish valley and surrounding hills and covers tiny pieces of America's two largest counties... both bigger than some entire New England states or Delaware. But the geniuses in the departments that control alerts have not figured out (with cellular phones going into their fourth decade) how to do keep me from hearing alerts and warnings for places that are a good 70 mph two hour drive away from me!
I recall the amusement and borderline anger of a group of about 100 when we attended a community project meeting in an auditoreum in Rancho Mirage, CA, when were all alerted with ear-piercing tones about a flood alert in Blythe, CA, 110 miles and 2 hours 30 minutes (at best) away!
In advance of very severe storms, my cell phone sounds the tones and gives weather alert via text, and during the Covid pandemic when they first began enforcing curfews, the county blasted out alerts to our phones every 2 days beginning with the tones, to notify/remind residents of the curfew.
I never got that type of notice during any pandemic stage, so that was a local decision I am assuming. The problem with systems like that is that they depend on the decision making skills and intelligence of public employees, often at "off-hours" when the quality of staffing is, well, sometimes doubtful
Also of interest - per the FCC, those services that broadcast alerts and messages do so voluntarily. The only ones they MUST carry, are Presidential alerts:
Emergency Alert System (EAS)
And even then, we are dealing with bureaucracy.