It's partly the problem alleged marshland and forest sequestration schemes face, alongside the assumption they're going to grow well in the changed climate.
(Limited experimental data suggests this works up to some 500 ppm as long as there's excess water and minerals. If the conditions are bad you lose capture potential. And what do you do with the methane releases from these systems? It's much more diffuse than from landfills.)
Actually, burning is probably the best way to deal with any excess methane. Methane has a significantly higher warming potential than CO2 does. So if there's any methane we're venting into the atmosphere, we should burn it to convert it into CO2. Bonus points if you can use the generated energy to capture the CO2 as well.
https://archive.epa.gov/climatechange/kids/solutions/technol...
If the landfill can generate electricity that would otherwise be generated, it will convert the CH4 more efficiently than a bus and you don't expand energy upgrading it.
You can power the bus with the already high quality CH4 you extracted from the ground that you would have otherwise burned in to generate the electricity.
I was reading somewhere that in buses in cold climates, heating is actually what eats up all the energy in an electric bus. ICE buses just use the waste heat from a combustion engine.
(Burning methane is even better as it releases much more energy per unit CO2 i.e. ~860kJ-per-mole-of-CO2 vs anthracite's ~400kJ.)
And as others have said, rocks actually are able to exothermally absorb CO2 permanently. It's possible to speed this up by grinding rocks to a powder, placing in water with a catalyst.
...none of this is to say I support relying on direct air capture and just go ahead and burn fossil fuels. We need to keep that in the ground and transfer the whole civilization to non-fossil fuels, otherwise if some populist jerks wer elected, they could just order the expensive direct air capture program to stop (can't do that if you're already transitioned to clean energy and all your wellheads and drills and coal mining equipment are rusted or melted down for scrap).
Source: [0] https://www.researchgate.net/publication/257177020_The_therm...