From the article:

The short answer is that it is clear from studies and from what we see with our eyes that ubiquitous sports gambling on mobile phones, and media aggressively pushing wagering, is mostly predation on people who suffer from addictive behaviors.

That predation, due to the costs of customer acquisition and retention and the regulations involved, involves pushing upon them terrible products offered at terrible prices, pushed throughout the sports ecosystem and via smartphones onto highly vulnerable people.

Here's a quote from one of the papers he cites:

several measures of excessive debt increase substantially. We find a roughly 28% increase in bankruptcies and an 8% increase in debt transferred to debt collectors. Similarly, auto loan delinquencies increase substantially as does use of debt consolidation loans.

Interestingly, we find that banks restrict access to credit on average in affected states. Credit card limits decrease and the ratio of secured to unsecured loans increases. After three years post-legalization we actually find a decrease in credit card delinquencies as a result.

Back to the article:

Putting gambling in your pocket makes the temptation to gamble ever-present. Even for those who can resist it, that is a not so cheap mental tax to pay, and likely to result in the occasional impulse bet, even without the constant notifications. First hit’s free. Constant offers that adjust to your responses, to get you to keep coming back.

Now consider that at least several percent of people have an acute gambling addiction or vulnerability. For them, this is like an alcoholic being forced to carry a flask around in their pocket 24/7, while talk of what alcohol to choose and how good it would be to use that flask right now gets constantly woven into all their entertainment, and they by default get notifications asking if now is a good time for a beer. You can have the apps back up and running within a minute, even if you delete them.

It was plausible that this was an acceptable situation, that people could mostly handle that kind of temptation. We have now run the experiment, and it is clear that too many of them cannot.