I thought that you observed blanket transfer into all corporations. This should not happen.
Both countries and enterprise try to keep their corporations afloat.
When there is low cash, they move money in (not into any public corporations, only fully owned ones).
The amount depends on the need for cash and profitable corporations will probably not need any.
Many times it happens when you purchase a lot of raw materials.
The feature is very old and has not changed in years.
It was created when players complained about bankrupted corporations, that could survive but needed a lot of cash to purchase raw materials for many months.
The number of bankruptcies decreased.
Corporations can bankrupt despite the feature, if there are sudden changes in cash and large negative cash. They can bankrupt before any transfer takes place.
The same happens in state corporations.
I general, we advise to keep up to 80B in the corporation and never touch it.
If it goes higher, there is a function on the cash page of corporations that allows you to set the cash level at some value for all corporations at once.
I do this once in a while and no corporations bankrupt.
If you have cargo shuttle building corporations you need to do so frequently as otherwise, they will all bankrupt.
(the problem is becoming smaller as the price of these products declined a lot).