Because no amount of money was going to solve the problem of people saying they think Microsoft's browser is slower/worse/etc. Switching to Chromium negated that in a way nothing else could.

When Microsoft beat Netscape with IE, it was by building a far better browser. Google is a stronger competitor than Netscape ever was though. Without Google dropping the ball (like Netscape), Microsoft would never exceed Chrome's performance by enough to be the fastest, most compatible (with Chrome), etc.

It is also just classic Microsoft when they are hungry. Like making Word use WordPerfect files and keyboard shortcuts. Only today it is that their browser is mostly Google, Linux is built into Windows 11, SQL Server ships on Linux, and their most popular IDE is open-source built on open tech (Electron) they didn't create.

When they get threatened, nothing is too sacred for Microsoft to kill or adopt.

We have enough people of working age now that hasn't lived through the Microsoft of old and don't remember what they can/could do.

Microsoft firing on all cylinders, when they want to, is a terrifying force.

I feel like they burnt enough browser goodwill with IE that no one who was on the internet back then wants to touch a microsoft browser regardless of the engine