When Microsoft released Window 3.0 back in 1990, there were very few Windows applications on the market. MS wanted Win 3 to be a success but their development tools were pretty poor. At the time, about all that was available to write Win apps was the Software Development Toolkit (STK) and a C compiler. The STK was little more than an interface to the Windows APIs, a collection of about 1000 function calls (many more than that today). Programming even a simple "Hello, World" program with C and the STK took over 60 lines of code. It was a painful process and very unforgiving. Botch an API call and you'll crash the system in less than a heartbeat.

In addition to the GEM GUI that you mentioned (a nice little GUI first released on the Atari ST series back around 1986 or 87), there were other GUIs that tried to win market share. There was one in particular that impressed me a great deal back in 1990. It was originally written for the Commodor 64 (!) in assembly language and then rewritten to run on PCs. It was slick, efficient, and did everything Windows 3.0 could do but it ran well even on 8088 processors. On an 80286, it really screamed. Unfortunately, they were very slow to release development tools, so this technically superior (IMO) solution quickly faded to become a footnote in computer history. At the moment, its name escapes me.

Better Windows development tools started coming out in 1991 or 92 with the release of Visual Basic 1.0. VB took off line a rocket because it made writing simple Windows applications child's play. Over the years, the visual technique spread to other languages such as Borland's Delphi. C++ provided object-oriented programming capability and an OO wrapper around the Windows API (Borland's OWL and Microsoft's MFC) and visual development tools were added for Borland C++ Builder and Microsoft's Visual C++.

Several companies were late to the mark with Windows versions of their popular applications. I don't think it was due to any plot by Microsoft. Instead, I believe part of that was due to complacency, part was due to them betting on IBM's OS/2 instead of Windows, and part due to the difficulty in writting Windows applications with the STK and C.

Lotus was over a year late and many millions over budget with their 3.0 version of Lotus 1-2-3 (the leading spreadsheet back in 1990). They didn't come out with a Windows version until sometime around 1992. By that time, Microsoft's Excel (a fine spreadsheet originally developed for the MacIntosh and later ported to Windows) had gained dominent market share.

WordPerfect bet on OS/2 and didn't release a Windows version until sometime around 1992. By that time, Microsoft's Word had gained a lot of market share. I never liked WordPerfect for DOS because there never appeared to be any logical pattern to their commands. I hated having to stop, look at the cheat sheet, find the appropriate Shift, Alt, or Cntrl Function key combo to do even rudimentary things. Word for Windows was a lot easier to use.