There are several reasons big company experience doesn't translate.
1. Legacy tech, "cool" big companies have the latest stacks but over time these stacks become old and the dev practices atrophy. The biggest cases of this I've seen are engineers unable/unwilling to do their own QA as its "not their job". Or unwilling to adapt to new technology the startup may be using.
2. Politics: Big tech companies have major politics leading to pathological "not our problem" conditions. Efficient and successful startups/scale-ups need to minimize politics, and some employees from big tech companies will have found this to be one of their primary skills.
3. Ambiguity/Timeline constraints/dealing with crap: At a big tech company everyone is expected to be at the top of their game and the company rarely faces deadlines that are not self-imposed. An engineer may expect 100% test coverage, crystal clear product requirements, and no risk of failure. Dealing with sub-optimal conditions is common in startups/high growth companies.
4. Definition of success: A big company may strongly value marginal contributions as prized wins. Shaving ms off of a frequent call can drive real monetary improvements when the company has hundreds of millions of customers. Making engineers marginally more productive has huge benefits when you have 50k+ engineers. Startups often just don't care about these things and simply won't value the skills necessary for this work in most cases.
On the flip side there are great engineers/managers who learned what made the big company successful and how to navigate internal obstacles. These employees are likely to be gold to a startup, but they are also gold to a well capitalized company with vastly more data on just how effective they are than a startup has. Odds are, startups are interviewing/hiring the employees the big companies don't care about - something the hiring firm often implicitly knows.
Why are big company employees not suited (or trained for?) to startup like environments?