INITIAL EXPENSE. Many software vendors will tell you if their software already contains 80% of your requirements. Does it make sense to build from scratch when only 20% of the development is left to complete? Don’t forget a software vendor can amortize their costs over numerous customers - you can’t.
If you decide to build and the project fails, you absorb all the losses. If you own it, you maintain it, along with all the associated costs. Once you start a branch in the code’s development, the more you develop that branch, the harder the migration effort will be to the next version.
EXECUTIVE BUY-IN. Many executives are hesitant to jump on the Open Source bandwagon just yet for their enterprise or revenue generating apps. Many technology savvy companies like Amazon, eBay and Google, aggressively use Open Source to develop solutions that provide them a competitive advantage. So can you.
INTELLECTUAL PROPERTY RIGHTS. Since Open Source licenses requires any software modifications be returned to the community, you forfeit your IP rights. If you distribute that application outside your company, some Open Source licenses may require you to make the entire application available as Open Source.
NO WARRANTY. If you use commercial software, the vendor has an obligation to assist you in a timely manner. Not so with Open Source. Unless you contract with an Open Source provider for support, Open Source support usually consists of community forums or you will need to figure it out for yourself.