“It’s because the law gave them too much leeway” doesn’t make sense. If you have leeway, you choose the easiest and cheapest method, not the one that involves building a whole new communication system. “They thought it was the only way to satisfy the law” also doesn’t make sense. There’s no reasonable way to get that from the law, they didn’t confirm it was necessary, and they didn’t publicly fuss about being forced…
2) There's likely a profit motive here as the software that is being advertised via this injected message costs money. They're likely getting a commission/affiliate fee from every customer that installs said software via this notice.