meaning of 'sell in'

“There are very few regulatory bodies,” says tech writer Paul
Armstrong. “And I think that’s why we’ve found ourselves in such
disarray recently … And if anything, it’s almost giving [businesses]
another free pass for another two or three years without repercussions
… It’s always going to move in advance of the regulatory framework.

“We have to think of it more holistically. But that’s quite hard to
sell in when economic times are tough … Could the change come from
actual car regulators going: ‘I won’t be buying your software, because
clearly it’s racist.’ So what is the pressure that you add to these
companies? I think the answer we’ve seen in history is there’s nothing
that changes [behaviour] as quickly as taking money out of people’s
pockets.”

This is from Richard Chataways The Behaviour Business.
What does bolded ‘sell in’ exactly mean here? To put into practice?