Well this deterrent isn't really working. Fare evasion is currently a big problem for the MTA (http://nymag.com/intelligencer/2019/03/mta-fare-evasion-one-...)

It's also not clear to me that it is ethical to have a punishment be far more extreme than a crime. Sending someone to jail for 40 days for stealing $2.75 seems a little extreme. That could easily turn a poor person with a job into a homeless person with no job.

A fine feels more appropriate. Maybe free rides for those who legitimately can't afford the fare.