Denying workers unemployment if they are legitimately entitled to it is frowned on and can lead to sanctions by most all the states unemployment offices. They are supposed to have posters in the workplace telling people about their unemployment eligibility. It is a federal program administered by the states, as official as minimum wage and other federal programs of this type. If they terminated an employee because of signing up on seasonal unemployment after working for them, that would be considered a bad thing.
Each and every employer of appropriate size and definition has to pay in unemployment taxes. The amount of these taxes paid by the employer is affected by several things. One of these is patterns of lay offs. In other words, employers who historically hire seasonal workers pay higher rates.
The number of people on the payroll, the unemployment rate of the whole state and nation, nature of the work, unemployment taxes is a fact of life for employers.Many large employers hire consultants who handle their unemployment, try to lower their tax rates by fighting claims, keeping up with paperwork. But I cannot count the number of times I have been confronted by an employer who has opened a seasonal business and is screaming because at the end of the season, his employees are eligible for unemployment benefits.
Yes, it could work out so that if a person has quit their long term high paying job, they could take a temporary seasonal job somewhere, work through the season, make what is called "re-earnings" and be laid off and be able to receive unemployment. (It's not a time frame, like six months you have to work somewhere, it's an amount of gross wages you have to make for it to be considered your separating employer. ) But unemployment insurance, even the maximum weekly benefit, is usually less than you could make working, even at a low paying job.
Most states have a provision that on each claim, if you have lots of employers in the base period and you left for a non-qualifying reason, such as quitting, or if you were terminated and unemployment was not approved, these employers are given what is called a "non-charge" to their unemployment tax rate, which means your drawing benefits doesn't affect their rates negatively.
Not signing up on unemployment when you would have been eligible is not by any means a virtue or a wise thing to do. No one is responsible for holding your hand and encouraging you to file when you might be eligible, but there is no down side to filing a claim, whether you qualify or not. No matter how many years you have been working, the only wages considered to set up a claim is the current base period, so you cannot save up unemployment benefits for use in future years. And you were under a misconception about unemployment that could have been cleared up very quickly with a little research.