The tax system is set up in such a way that people are limited in what deductions they can make with respect to employment income in general. Most expenses related to employment income are not deductible unless they're specifically enumerated exceptions in the Income Tax Act, whereas business is more of a bigger picture of what expenses are relevant to computing the profit of a business, and that builds off accounting principles. It's really a difference in the way the system is set up. Deductions like this one, the deduction that was in Bill C-19, are really exceptions to the general rule that employees are not able to claim deductions against their employment income.
On November 2nd, 2022. See this statement in context.