Software development varies enormously. Flight avionics software differs from video game software differs from a spreadsheet differs from an order-entry system

Software development varies enormously. Flight avionics software differs from video game software differs from a spreadsheet differs from an order-entry system differs from laboratory analysis software differs from a web browser and so on. Flight avionics differs from a commercial jet liner to a fighter plane to a model airplane. Some projects have huge budgets and others have shoestring budgets. Some projects require extremely high reliability and quality; cost is not an issue. Other projects can be quite buggy, low quality but still useful -- cost effective. Developers vary as well. Some temperamentally find something like TDD useful. Others do not. There is no one software development methodology to rule them all.