Yes, you are right. I own several rental houses myself (not in New Jersey). Rents are increasing in my area too. If I have a good renter, I try not to increase his/her rent or, if I do, I only do so gradually, even if this means getting below-market rates. But, when someone moves out, I charge market rates to the next renter. This makes sense ethically (I don't want to price anyone out of his/her house if I can avoid it) and business-wise (a below-market renter who pays his/her rent every month is better than taking a risk on a new renter that might not be a reliable payer). The problem is, many rental properties are owned by large corporations (hedge funds, etc.), that prioritize ROI over all else.

I think you hit upon a big part of the problem when you said "a New Yorker will pay it if a Jersey citizen won't". Your proximity to NYC and the high cost of rentals in NYC is means that Jersey citizens are competing with NYC residents for housing, and this drives prices up.

I wonder if the pandemic and so many business allowing employees to work from home increased the number of people who work in NYC who were willing to move to New Jersey in order to save money on housing. This would have caused an increase in demand for rentals in New Jersey and resulted in higher rental fees.

There are possible causes for the high cost of rent other than the landlords becoming robber barons:

1. Insufficient supply of housing. In some parts of the country, zoning laws and permitting processes discourage developers from building affordable housing.
2. High value of houses. If a house has a high market value, landlords will charge a high rent to ensure that they are earning a decent return on their equity in the house.
3. High property taxes. If the property owner is paying high taxes, he/she will need to charge more for rent to ensure that property taxes can be paid.

Obviously these causes can work together - an insufficient supply of housing will drive up the value of houses, and these two causes together will cause rents to increase.

I have no idea which (if any) of the above apply to New Jersey - you might want to research zoning laws, building permit policies, and real estate taxes in your area.