I don't live in Seattle, so I don't know what it's like there, and nor am I an expert in physical security. However, if it's a social norm to pay for human parking attendants, it's not a stretch to assume that there would be human police officers around too. Ultimately, you can't have people doing some jobs without other people doing supporting jobs, but the same is kind of true for digitalisation too: the reason these parking systems are so disliked is that we don't have a conventional or standard parking charge infrastructure to support it yet.
I'm sure people would be much happier with paying for parking via the internet if it was done with an open, reliable and secure protocol with plenty of easy-to-use implementations. But given how impossibly far that is from the digital systems that are used for parking currently, human parking attendants seem to me to be an attractive option. My original comment was 'radical' when seen from the current standpoint of industries being so 'anti-human' that they won't employ workers even when labour is cheap, the work is humane, and it improves the experience for the customers.
So I've no idea if it would be a good decision for Perfectly Profitable Parking LLC, but I think it would be a good decision for the world :)