In the UK, most people who are employed do not file taxes, they are handled by the employer. Other people whose only income is benefits also do not file taxes.

I think it's safe to assume that GPs suggestion includes people who are paying taxes via the employer or receiving benefits. Also, in lots of countries employers already subsidize public transportation costs.

It's also possible the suggestion is based on the concept of a country where 'filing taxes' is some optional or culturally odd thing so people need to be incentivised to do it at all. Or perhaps it's more thinking along the lines of 'someone who is a citizen' and measuring that by using tax filing as proof.

I read it as a "reward" and incentive for filing taxes in places like the US where everyone has to do it so it wouldn't translate to somewhere that taxes are paid via the employer or people on benefits because then there is no reward.

Adjust it based on the country’s tax system, but in Canada it would work because the employed and those on benefits tend to file taxes.