Is there a cap on H-2B visas?

Yes, unfortunately there is an H-2B cap. There is only a limited number of H-2B visas per fiscal year (October 1 – September 30). Currently the cap is at 66,000.

Unlike the H-1B application process, the H-2B application process has two application periods:

33,000 H-2B visas are available for the first half of the fiscal year (October 1 – March 31)

33,000 H-2B visas are available for the second half of the fiscal year (April 1 – September 30)

If the cap is already met you will have to apply for a different visa category (e.g. E-1/E-2 or L-Visa). Of course you have to check your eligibility for either of them first. Or you have o wait for the next half of the fiscal year before submitting your application.