Tax avoidance is mostly happening because tax rates are seen as too high by the rich. Paying 40% tax on $50,000 is different to paying 40% tax on $10m. Past a certain point, setting up an avoidance mechanic (if one exists for the investment you want to make) will be cheaper than actually paying the default tax rate. Avoidance can never be stopped, because it's mostly structuring transactions in legally allowed but clever ways and you can't stop that (or you would block normal, legal transactions as well).

Say I have $10m I want to invest in an international company. If I do it in the most obvious way, by capitalising an entity, I might get a 30% return on my money after 3 years after paying all taxes. Alternatively, I can structure it in a different way, and make 50% in 3 years, because I end up paying less tax. The difference is an extra $2m on $10m. If the amount to set up a structure/attorney fees/possibly litigation fees < "normal" tax to pay -> avoid.

The only real solution is to lower rates across the board by getting rid of most deductions. If you remove the incentive to avoid, it'll be less worthwhile to avoid, and most people will stop doing it. How much people would put in an effort to avoid taxes, if the actual tax rate was, say 10%?