There's no single reason that covers all situations. Here are the ones that come to mind:

1. Labor of love - Some developers make games purely for the enjoyment of creating them and want to share their results with others.
2. Building a player base - In some instances, a developer may choose to release a game for free as an initial step toward building up a player base for a later game. In particular, crowd funding efforts are often more successful when they launch with a strong first day; giving a game away one way to build that day one audience.
3. Building a portfolio - One of the best ways to demonstrate that you can make games is to demonstrate the games you've made. Some people start with releasing small free games to build personal experience & reputation.
4. Reducing work - Unfortunately, as soon as money becomes in involved, some things become more complicated. Users expectations for support increase. There's often more paperwork & book keeping to deal with taxes, income, etc. Some developers just want to focus on development, not business.
5. It's only free today - Not all games stay free. Some platforms give developers the option of changing the price. Some may release for free initial (for instance during early access) and la

There's no single reason that covers all situations. Here are the ones that come to mind:

1. Labor of love - Some developers make games purely for the enjoyment of creating them and want to share their results with others.
2. Building a player base - In some instances, a developer may choose to release a game for free as an initial step toward building up a player base for a later game. In particular, crowd funding efforts are often more successful when they launch with a strong first day; giving a game away one way to build that day one audience.
3. Building a portfolio - One of the best ways to demonstrate that you can make games is to demonstrate the games you've made. Some people start with releasing small free games to build personal experience & reputation.
4. Reducing work - Unfortunately, as soon as money becomes in involved, some things become more complicated. User's expectations for support increase. There's often more paperwork & book keeping to deal with taxes, income, etc. Some developers just want to focus on development, not business.
5. It's only free today - Not all games stay free. Some platforms give developers the option of changing the price. Some developers may release for free initially (for instance during early access) and charge for it at a later date.