Have a Doubt about Transaction fees !

From schweser -” Transaction Fees - These are fees paid by third parties to the GP in their advisory capacity ( for investment banking services, such as arranging a merger). These fees are usually split evenly with the LPs and, when received, are deducted from management fees”

i don’t get it. Does this means GPs also do investment banking activities?? Like advising M&A n all? I used to think that advising is exclusively done by investment banks to PE Funds and Portfolio Companies…

any help would be greatly appreciated.