Actually that is my current strategy. I make twice the average salary for my country and my monthly spending is around the minimum salary. Everything excess is going on a savings account, which currently has the equivalent of 100 average salaries. I plan to retire early or take few years off.

The main thing preventing that for a good part of the population is that it's quite difficult to earn enough for it to last for the rest of your life. Conservatively you need about 30-40x your yearly spending in the bank to never have to work again. Say you need about 15000€ a year for rent, food, entertainment and other expenses. You'd have to save at least half a million euros to afford that indefinitely. Most people never manage to earn that much excess income and those who do are likely in a demographic that enjoys what they do and would continue working.

>If so, what has prevented you from saving all the excess money beyond minimum salary and retiring

I don't see what this has to do with UBI, other than maybe you're trying to counter the presented hypothetical by asking if the parent poster would actually be happy to live frugally.

Not only are there plenty of people with professional success that save aggressively or have other goals (e.g. skiiers that makes six figures and still live like skibums), but they're a different category than people that would be willing to coast by minimally if given the opportunity.