The purpose of having the temporary foreign worker program in itself is to address labour shortages where Canadians aren't available for an occupation. An open work permit allows anyone to work in any occupation. You might bring somebody in and think they're going to work on farms, but they could work in any other sector. Having a sectoral work permit would ensure that you have individuals working in the sector that has the shortages but with the ability to move from employer to employer.
On November 9th, 2023. See this statement in context.