Let's go back to 1995, you're a corporate IT manager or C-class executive , responsible for deploying desktops, laptops, to 10,000+ employees (I worked for or with several companies like this at the time).

You need directory services, email, app deployment. You also need common office apps, like word processing, spreadsheets, etc.

Your end users are finance folks, regulatory compliance teams (i.e. legal), marketing, etc, who've been working with systems that are purpose-built for their roles (mainframe/IBM As series for finance, print layout systems for marketing, etc), with not everyone really using email much.

Suddenly you have an opportunity to migrate everyone to a general purpose system that's pretty easy to understand, and many people already have some familiarity with. You can eliminate sending handbooks to everyone by building your own intranet which people can access with IE. Your HR systems (which are still on mainframes/AS-400) can now be accessed by IE from anywhere in the company, so time entry, vacation, benefits changes, etc, reduce time and paper consumption dramatically.

Theres a million reasons why companies embraced Windows back then. Standardized UI for everything massively improved support capability. Being able to take output from legacy systems and present it better either via IE or custom-built apps made for significant training reduction, and could even reduce password management difficulties, and increase password compliance/security for the legacy systems (I saw one custom app in 1996 that presaged SSO by managing logins to 11 backend systems).

There was nothing in the *Nix world at the time that could compete with the whole package that Windows/Exchange offered, for the user management and end-user ease-of-use. Especially since you could retain your legacy systems and use Windows as both Windows and as a terminal if needed, and provide app flexibility for end users.

Then there's the productivity side, there were already tons of Windows apps available, with many more on the way. And people were familiar with how to use them, because of a standard interface. Also, many people were using Windows at home or school, so we're familiar with it.

Just compare Word to Wordperfect at the time. I'm not sure WP was even a GUI yet (I forget when they added it). So legal folks were fast as hell with WP, but your average user wasn't, and it had a bit of a learning curve. Compare that to the menu-driven, WYSIWYG Word Perfect.

Now look at the SMB space, where money is even tighter. It's much easier to deploy and manage an exchange/windows setup for 50 users than what, setup a Unix system? I could teach someone to do day-to-day Exchange admin stuff in a few hours, because GUI is way easier than command line for people who are new/inexperienced, because it reveals the concepts/paradigms. And Exchange ran on fairly generic hardware. Again, they didn't have to buy something like an AS400.

Unix folks just didn't see what was coming for some reason. I remember Unix admins disparaging Windows as a "toy" in the early/mid 90's. Even today I couldn't imagine selling a Linux setup to most companies, as mature is it's gotten.