One of the biggest issues is explaining it to the public in a way that makes sense and will be widely accepted. To start the opposition and the media will instantly claim that whoever is proposing it is going after people's money, especially if Labour are proposing the idea. On top, as I mentioned above, people in this country often vote with their wallet and think extremely short term. They would rather have a little more now and probably waste it, than invest in a comfortable retirement. This also applies to improving public services as a whole. For some reason in this country we seem to expect getting more for less and it just isn't viable. However, that doesn't stop people getting outraged when someone suggests taxing them more to make a better society. Look at the guy during the last election who was shouting at the Labour MP because he thought he wasn't in the top 5% of earners at 80k a year. He didn't have a clue how much less the majority of the people in this country earn and only saw it through his narrow lens. Of course he doesn't think he's rich, because the majority of people he probably works with or is friends with earn similar or much more.
The real problem is that we have created a political and financial system that is based purely on looking after yourself. Politics has slowly become more and more negative with politicians talking less about what they would actually do, but about what the opposition would do. Vote for us because if not the other guys will do this. As well, this is made worse our FPTP system which again recent evidence has shown it is creating more negative politics. Tactical voting where you don't vote for the party and policies you want, but the party most like to keep out the party you don't want. That's if you're lucky enough to be in a constituency where you vote can actually make a difference. You then combine this with a financial system that only measures growth and GDP to show how well an economy is doing.
This article here does a good job summing up the problems with this system:
https://www.theguardian.com/comment...rics-gdp-economic-performance-social-progress
Our society is completely structured around people's individual wealth and doing what is best for yourself and your family. It's not sustainable and, especially with the climate crisis, it will all coming crashing down quite soon.