"factors behind" is a fully grammatically correct phrase and can be used in written English.
For example, you can say "There are a number of factors behind the success of this organization."
The factors behind their current separation are not known.
Investec said: "There are several factors behind this reduced guidance.
There are multiple factors behind this Eurocentric phase.
The report casts light on the factors behind innovation.
Certainly, there were other factors behind this boom and bust.
Mr. Romney said the low-key atmosphere and watersports were the driving factors behind their purchase.
Among the most important factors behind I.M.'s quick conquest of the business world is geography.
This current stretch of good times, however framed, clearly has many factors behind it.
ISIS is a horrible group doing horrible things, and there are many factors behind its rise.
Less clear is the factors behind some of the surge in demand.
Expansion of the major supermarkets is considered one of the biggest factors behind high street decline.
