Microsoft bundled Internet Explorer for free with Windows, essentially destroying Netscape’s business overnight.
1) Browsers were destined to be a commodity, given the first browsers (like Mosaic) were effectively free, and even then it was clear that a browser would be as critical a component of a consumer OS as, say, a file explorer or a calculator.
2) Netscape simply was an inferior product compared to IE and other browsers like Opera (which survived despite IE being free and Microsoft's shenanigans, and is a thing to this day.)
The book of the battle - Competing for the Future - makes it clear how much of a mess Netscape was in internally
Essentially they had alternate code bases for every other version of the browser and we forever porting feature and bugs between the two (and often forgetting and so getting regressions)
https://lowendmac.com/myturn/02/0403.html
(Edited to add, another more detailed article: https://macfolkloreradio.com/be/)
People make this claim about a lot of software (Netscape being the poster child) but typically whenever I look into it, the nuanced answer turns out to be "Microsoft may have thrown it's weight around, but the product largely failed on it's own merits."