Stupid, wait...let me check my bank account that stupidity has brought me....7 figures and growing....so I guess not recommending free crapware has made me very rich.
When speaking in terms of quality networking software, using the term "crapware" to describe Linux and packages like pfsense shows how ignorant you are... Properly configured and secured, I can make a Linux or BSD box do everything that you can do with a Cisco router and more.
And Cisco only uses linux on its VOIP and consumer products. IOS (found on its enterprise firewall and router products) is a hardened operating system and the backbone of the Internet core routers.
Apparently you don't subscribe to the CERT lists because your statement about IOS being "hardened" is anything but true...
As for manufacturers using Linux... Several competing manufacturers are using OSS as their base router OS. For example, Juniper, which kicks Cisco's ass, is using FreeBSD as the OS on their routers. The CLI is just a userland that runs ON TOP of FreeBSD.