You need to open your eyes. What you're saying is like asking for 15 years of work experience from a talented 20 year old in a job interview.
It completely dismisses young, upcoming managers who would potentially have what it takes to rebuild United, in favour of ones that could easily be failures, but have won things mostly because they've been around for a while.
This "winner" and "winning culture" thing is overrated as well. There are plenty of managers who will win CLs, ELs and league titles within the next 10 years, who are completely unproven and unknown with an empty CV right now.
Alonso hasn't won anything, and yet is considered one of the best upcoming managers in the world. There are others like him out there too.
Guardiola was already a great manager in Barca B, just hadn't had the opportunity to prove himself on the biggest stage yet at that time. Same as Wenger in Nagoya, Sir Alex before United and Aberdeen, Klopp at Mainz, Arteta being Pep's assistant at City, Mourinho before even taking over Porto, etc.
Trophies and a good win-rate is always a good thing, but when a manager doesn't have one or both of them, it requires a lot of context before you can draw conclusions on their ability. It doesn't just mean that they simply aren't up to managing a big club like United.