The truest saying in software is that the highest value output of a project is an engineering team that understands your business. Past a certain point of size/complexity you can't buy one of those for any price, you have to make it.
Outsourcing turns an investment opportunity into an expense.
This rings true for my experience as well. And it also highlights the waste that occurs when a successful team finishes delivering and is immediately dispersed to the four winds, something that happens all too often.
That's why companies end up requiring "extensions" over and over for consultants. I know people working for consultant firms that have been with the same client for more than 3 years.
Where to outsource is the right question. I could write a word processor, but my company just buys me Microsoft office. My company could buy the software I wrote from an outsourcer, but we consider it a competitive advantage to do it in house.
Buying a product is different than paying someone to make a product for you. Since your company is the only customer for that product there is no benefit in outsourcing it other than the ability to rent a developer (contracting might be a better option). Nobody else is going to buy that product.
Outsourcing turns an investment opportunity into an expense.