You don't matter...
...so naturally, there is no need for enthusiasm. The bosses don't care who works for them, they just need warm bodies that will work for a pittance (so they can fatten their own checks). There are literally hundreds of people that can do your job and will work for less, they are just waiting for the chance.
If you are enthusiastic and happy in your job you may stay and, gasp, ask for a pay raise. You staying, and making more than a newbie base rate is counter to them making more money. Then they have to increase your vacation time, more money right out of their pockets. The new hires generally come in with a decent attitude and minimal lip service will keep that going for three to five years until they start costing the company too much money, in higher pay rates and more vacation time. Then it's time to find the next flunky.
Who needs enthusiasm in the workplace? It is counter to their goal of keeping payroll low, and performance high. But most importantly, it impedes the bosses ability to fatten his/her check because, lets face it, you cost too much.
With all the advancement in technology, the need for truly skilled workers has waned. With a few hours of training we can find some poor schmo to do a job; do it for less pay; less vacation; less sick time; less demands overall; by in large, there is no need for a 'Knows it all' employee.
Managers, Executives and Owners only care about one thing, fattening their own wallet (and/or the wallets of shareholders). Your happiness runs counter to their goal. It really is as simple as that.
This is the era of Ebenezer Scrooge and we are Bob Cratchit.
