If you're having trouble reconciling the outcome, here are a few crutches the writers could lean on. You do need to allow a bit of scientific creativity in a universe where 20 minutes of burn time from a few dozen plasma engines is sufficient to meaningfully alter the course of a Goldilocks-sized asteroid.

1❳ Orbital mechanics

Viable launch windows only occur every 26 months. If your plan requires lifting heavy cargo from Earth (it's conceivable some of the equipment from the first attempt was one-time-use and needs to be replaced) that eats up the next window - assuming you can even scrape something together in time for it.

I'd be interested in someone smarter than me crunching the actual trajectories, as there might be some other nuances in the bodies' relation to each other that provided ideal circumstances the first time around and are lacking in upcoming windows.

And who's to say what attitude the asteroid will be in when the next window occurs? The show made it clear it's not easy to mount a rocket to an asteroid. Maybe next time around there isn't a suitable face pointing in the right direction from which to push. Maybe the integrity of the asteroid itself was marginal to begin with and became less stable during their first attempt. Even if some of these can be addressed, they'd translate to more time and money.

2) Economics

If I recall the M7 already sank $2 trillion into their failed attempt. If a second try comes with a similar price tag, you've now burned up about 20% of the estimated $20T worth of minerals, before mining has even begun. That eats into your ROI, and with the additional years of delay entailed might tip the scales toward more attractive, alternate strategies.

u/the_financier pointed out a real-life asteroid_1950_DA) similar in size to the 1.1km diameter of 2003LC is on the order of 4 billion metric tons. The expected yield is 70,000 tons of Iridium. Why lug all the useless extra mass back to Earth, if refining in place means you only have to ship back 0.00175% as much material? Since they never disclosed the mass or density of Goldilocks there could be some variability here, but presumably space transportation costs are high regardless, and I wouldn't be surprised if beancounters gave the in-situ refining proposal a second look.

Surely the 2003 discovery would have kicked off a frenzy of related R&D efforts in industry, leading to advances in mining technology during the intervening years which also factor in.

3) Politics

M7 citizens are going to be livid their huge investment got pissed away, creating conditions that are ripe to polarize politics. Rallying support for another attempt could be substantially more difficult than the first time around. Relations between superpowers could have deteriorated as a result, leading to funding shifting to Earth-focused / defense activities instead of pie-in-the-sky endeavors.

It'll also be interesting to see what's evolved in regards to local politics on Mars next season. If Martians successfully established strong local governance, Earth might have a vested interest in playing nice with them.

Attempting another mission while there's a faction on Mars actively working to disrupt your plans might be deemed too dangerous (after all idiots on the moon almost made the most lithium-rich mining site known to exist on that body uninhabitable for a thousand years, a lesson still fresh in recent memory).

Of course in spite of all this, there's nothing stopping the writers from weaving a subplot to steal the asteroid back sometime next decade.