* abundance of people with Cisco knowledge and certifications, everyone has fiddled with a Cisco CLI at some point in their career

* devices on the gray market are very cheap, low barrier to entry for setting up a lab or a SMB infrastructure

* the lower end stuff is pretty much set and forget (e.g. we still have 1700 series devices from year 2003 routing calls without a hiccup)

* "nobody ever got fired for buying Cisco" company mentality