Likely because SimCity was a memorable game that can be associated strongly with that era in our nostalgia. But also, not something "serious" such as tools designed for work or productivity.
Having MS design Win95 with specific hacks for SimCity means that MS thought that SimCity was special and important, which reminds people in that era that they also thought SimCity was special and important -- and it's mildly or moderately interesting enough for these people to find "behind the scenes" work which validates their nostalgic memories.
SimCity games had long shelf-lives and were on the sales charts for years. It could be it wasn't individually special and it was just "make sure the top 20 windows games work".
Microsoft had a program internally within it's development teams for Windows 95 that you could get any software for free. You just had to agree that you'd ensure it was compatible with Windows 95 and take ownership of its quirks to get it to run on Windows 95.
I'm familiar with SimCity and Raymond Chen. So familiar to know that SimCity was one of the top-selling Windows (not DOS) games. So while you and I and everyone loved SimCity, Microsoft had the economic motivation to make it work. They also certainly put more effort into obscure business software nobody remembers.
Per wiki, they released "SimCity Deluxe CD-ROM" for Windows 95, so the game was obviously still selling well even then.
Having MS design Win95 with specific hacks for SimCity means that MS thought that SimCity was special and important, which reminds people in that era that they also thought SimCity was special and important -- and it's mildly or moderately interesting enough for these people to find "behind the scenes" work which validates their nostalgic memories.