It's not a matter of I.T. guys not taking the proper steps.
It's a matter of price versus "what if". YOU try to convince a pointy haired boss to spend thousands and thousands of extra dollars on something that "may" happen.
It's often hard enough to convince higher ups to just upgrade old infrastructures that are maxed out on resources. Even if you have proof of issues or near failures. The ONLY time they will happily spend money on upgrades and making your infrastructure more robust is after there has been a critical failure and they actually see their bottom line being hurt and even then if you don't get the approval and dollars fast enough, you run the risk of "What are the chances THAT will happen again?"
More often than not, infrastructure is patches built on patches, one I.T. guy coming in trying to "correct" mistakes of his/her predecessor (who they then realize was working with an underwhelming budget), THEN realizing that it's such a mish mash of bubblegum and duct tape, that any serious fixes would require serious downtime with a complete overhaul. Otherwise you run the risk of the whole thing imploding like a blackhole.
How many I.T. guys seriously have the guts to walk up to their boss after being on the job for only a week and say, "I need 50k and you're network will be going up and down for two weeks as I rebuild and fix it all."
I tried it. I, however, had the ammunition that my company went from 3 people to 40 people in 18 months with another 20 predicted in the next 6 months and that the two box servers were maxed out AND that we were renovating a newly purchased building so we could plan everything from cabling, to telephony to security and future planning for 250+ people.
It also didn't hurt that my boss knows that I.T. is an investment when done right and NOT an expense. Even then with everything on my side it still took 3 months of planning, proving, mapping, designing and quoting from vendor after vendor before approval went through.