The significant environmental factor is that many planes have been sitting idle for months. This is exceptionally unusual in the life of most airframes. Idle time is an opportunity for parts or fluids to settle in a way they might not otherwise.

For example an extremely slow fluid leak could be “reset” every time the engine is operated. Allow time for fluid to accumulate and suddenly there’s enough fluid where it shouldn’t be, perhaps causing just enough mechanical stress to exacerbate an previously unknown wear point or design flaw present in a tiny minority of copies.

(Of course this hypothetical flaw couldn’t cause catastrophe on first flight, as that is generally an empty plane travelling from long term storage back to the airline’s hub airport. The flaw would have to subtly weaken a part which then fails after multiple rounds of uneventful flights.)