Two things.

Firstly, ... a country needs exports to obtain foreign currency to offset what their cash needs to pay for imports. North Korea has exports worth about $3 billion, and nearly half of that is from coal.

So if the hacking activity in North Korea brings in annually $300M worth of bitcoin (which can be fairly easily converted to other currencies), that puts "hacking" among North Korea's largest exports, possibly the second largest export.

Thus the country essentially has essentially not just an incentive to maximize its hacking capabilities, but the necessity to do so as strategic priority in order to pay for imports.

Secondly:

Talent is equally distributed. Opportunity is not. ~ Leila Janah

The talented technical minds from North Korea are likely getting pulled into hacking, disproportionately. While westerners don't freely travel into North Korea, ... certain North Koreans do travel into other countries (Russia and China) for training and such. One of the Tweets describes that:

https://Twitter.com/thedefiedge/status/1545093516920889346 https://nitter.it/thedefiedge/status/1545093516920889346

So essentially, in a dictatorship, if the leader wants a sophisticated hacking enterprise, the leader gets a sophisticated hacking enterprise, at the expense of other priorities (whose potential talented candidates were re-assigned to the hacking endeavors).