Water ingress isn’t the issue & there’s been waterproofed ports for decades. They wanted to make devices thinner—but what value is it when its too thin to support a jack & made of materials that now require a case?
That's probably just the marketing reason. The realistic reason is probably that they want to sell you their brand of wireless earbuds that need to be replaced in a few years tops
Which is only likely to last one year anyways. After which, you can pay an exorbitant amount to replace the degrading glue. I'd just like my wired headphones back, the jack will last longer than a year at the very least.