Microsoft products, including the browser, are still the primary target for hackers, because they're used by default by people without technical knowledge.
I have technical knowledge, but I don't want to spend my day deciding whether each interaction with the internet is an attempt to hack or social-engineer me.
Although, yes, professional hackers are quite likely to include support for hacking Chrome or Firefox or whatever in their toolkit. But the volume is less.
Microsoft products also have (semi-)secret access to Windows internal functions, which means that more damage can be done by hacking than with a third-party browser or e-mail product.