The difference is a) the FTC was way more lax in enforcing anti-monopoly laws than back in the day, b) Microsoft was a monopolist, c) downloading software from the internet hasn't been as much of a thing back then, so obtaining internet explorer replacements was more complicated, so preinstalling something was going to influence pepole's descisions way more than now where installing an app is just one visit to the app store app away. Only years later with improved internet speeds for everyone we got the ability to install chrome with a simple download. Lastly, d), you also have to consider that Chrome and Chromium based engines basically have a monopoly right now. So I'm not sure what the government stepping in will bring to users: Right now it's more that Safari is the only non-Chrome browser that most web devs care about.

Re b: Apple has never been a monopolist so they never got into that situation. This allowed them to have such opinionated choices that would have never worked for Microsoft. However, this might be changing. Recent statistics show that they have extreme market shares in the teenager demographic. If those kids grow up and keep buying iPhones, Apple will become one, in the US market at least, and this means they will have to change.