Several reasons:

1. Traditional low pressure systems weaken as they approach the Appalachian Mountains. Pittsburgh is basically the start of a very lengthy mountainous area, hence the scattering of a lot of storms.
2. This one’s obvious, but we are out of the lake effect snow belt. This is not news to anyone except tourists who think we get a lot of snow. BUT these micro lake based systems end along route 80, AND mess with the air pressure of larger storms traveling East-west, or the fast moving “clipper” storms from the North.
3. We’re still not that high up in elevation. We are a mountainous city, but not high up in the Laurel Highlands enough to get a ton of snow squalls to make up for that… often that results in a 10-15 temperature difference between here and the Seven Springs area, which impacts snowfall greatly.
4. We are too far west for Nor’easters. These are this big news-worthy low pressure systems that start in the south and move north up between the Appalachian mountains and Atlantic coast. These are those awful blizzard style storms that take all that moisture from the south and then dump feet of snow along the coast. We’re too far west for that!

Here’s a crude image kind of showing these concepts:

https://i.imgur.com/ofzRVRJ.jpg

Thanks! That was a good read- what an exotic little slice of Pittsburgh life