[the8472]

If you do everything over UDP then you have to reinvent a lot of what TCP brings to the table, in every single application. The most critical part is congestion control. And people are bound to reinvent or reimplement those parts poorly because most high level programming language standard libraries don't expose all the ancillary socket data you would need to get the header data (e.g. ECN flags or MTU). With all that complexity you will be back to worth several books, but this time you don't just need to be able to use it but also maintain it.

For many usecases TCP works well and you should avoid adding another dependency.