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.