Except for the logistics, such as funding, brain drain, social attention/PR. Frankly, I don't think we could "improve Earth" effectively without major restructuring of power, resources, social attitudes, etc., even if massive amounts of resources were thrown at it. People would rather work on space exploration because it's more exciting and hopeful.
This is classic zero sum thinking. A dollar more for space is not a dollar less for the environment, and one more aerospace engineer is not one less environmentalist.
You might as well argue for a global ban on dancing or fun because it is a distraction from improving the earth.
So are you saying that when random billionaire #38 puts in $5 million to space ventures, they're willing to also give $5 million to the environment? Although just throwing money at the environmental issues is a lot less effective than powerful people, like probably those billionaires, reforming industrial practices and whatnot. Like eliminating disposable plastic bags. Positive-sum games aren't always accurate either. The issue with always-upward economic and technological thinking is that, if (when?) the bubble bursts, we realize that growth can't come out of nowhere. Even if it's just a matter of psychological motivation and not money, it turns out that people can't just focus on twenty causes effectively.
> when random billionaire #38 puts in $5 million to space ventures, they're willing to also give $5 million to the environment
It was never going to the environment. It was going into space ventures or into some consumer play. There is practically zero competition between space and environmental concerns. (To the extent environmental concerns compete for resources, it's with discretionary social services. Similar donor bases. Similar line items in most national budgets.)
The engineers working on rockets wouldn't pivot to environmental sciences if we closed off space. Some would go to defence. Most would go to random other areas, likely those that pay well, like finance and that consumer play the aforementioned billionaire funded.
> people can't just focus on twenty causes effectively
We're investing more into crypto than we are into space.