Due to the UK political system not having proportional representation, it's incredibly hard to get anywhere setting up a new party. Almost impossible. Look at the percentage of the population who voted for each party at the last few elections compared to the percentage of seats they got for that vote and you'll see the problem.
So people join the "main" parties. And necessarily become corrupted/ disillusioned before they can get anywhere near the top, by the various interests that fund them all. Anybody in it for the "greater good" is weeded out by the systems and cliques in the political parties.
On top of that MPs and their families are subjected to media attention, online abuse and death threats, a very stressful job and inflexible working hours for £70k ish per year, far less than a full time GP earns. Or anybody even fairly senior in their professional career in medicine, finance, economics, accountancy, law, education, etc. So you can see why it isn't attracting talented people. Why would someone put their family at risk and quit a stable career for the prospect of maybe getting a temporary job for 5 years with a lower salary?
In most comparable countries that equivalent of our MPs earn perhaps £200-300k per year. Even that is low because it's public service - a comparably responsible role in industry would pay far more. If you just take a look at the MEPs sent to the European parliament by other EU countries: ex-Prime ministers, ex-diplomats, highly skilled people. Compared to the trash we sent - Farage etc. 
So embarrassing. And Westminster is no better. The quality of people in politics now - in terms of intelligence or decency - in general is shocking if you look back and compare to previous decades.
The best thing would be to put in place a PR system, ban private funding of political parties, and triple the salaries, paid from tax money. It would be a pittance in terms of the public finances but clean up the system, make corruption much more difficult, make the every vote matter, be more likely to lead to balanced evidenced-based governance, genuine discussion of things that matter instead of mindless slogans, and potentially then attract people with actual skills and a conscience rather than clueless public school boys and billionnaires (Sunak) who think it is all a bit of a joke and a stepping stone to getting their name in history books and being invited to speak at dinner conferences for £££££ of getting lucrative directorships from their "mates" when they leave office. But that's why it doesn't change because to change it those same people would be required to vote to change it. I mean, Rees-Mogg's father wrote a book about how to make money from disaster capitalism called "Blood in the streets". 
It's all fixable if the public put pressure on to have it fixed but most have so little understanding of how it functions that they won't, so it stays the same. I wouldn't get involved in it how it is right now, if I were you. I understand the frustration and wish to change things, but the above is why nobody with any decency or sense of will go near it with a bargepole. So it continues....
Sad I agree.