NIH (Not Invented Here). The reluctance of
people to use software that was not developed in-house. There are often good reasons
The developers of the package you buy may simply drop the project. Without
source, you are stuck.
Even when the source is in escrow, you don’t know its quality.
The developers may destroy the project with featuritis or take it off in a
direction irrelevant to your needs.
The developers may start jacking up prices for the program or support, or
demand obscene royalties on your distributables.
There is no control over what bugs are high priority to fix.
The code may be bloated with features you don’t need.
On the other hand the advantages of buying software are:
It is usually all ready to go. In house software will need to go through quite
a rigmarole before it is ready to use.
It will likely be cheaper since the development cost is spread over many
Costs are known in advance.
There are more eyes looking for bugs, so they will likely be discovered
It would probably be unwise to develop an SQL (Standard Query Language)
engine in house. There are so many to choose from. If one failed you can fairly
easily flip to another. On the other hand it probably be unwise to buy a general
purpose billing package for a large company. There is so much customisation required
you might as well start from scratch.