Does the auction happen automatically during Crowd Loan?

Question

During an auction crowdloan for propsective parachain, does the auction run automatically? Or do we need to manually make a bid?

If it is manual then why doesn’t everyone go all in at the beginning of the auction period?

Answer 1

Adding to William's answer, here is an example that shows the bidding in action. When a campaign receives a contribution, the bid is automatically placed with the updated balance. In the screenshot below, you can see the block numbers at which bids have been automatically placed due to crowdloan contributions

https://polkadot.js.org/apps/#/parachains/auctions

Answer 2

A crowdloan automatically places a bid in the on_initialize hook (e.g. every block) after entering the ending period if the raised funds have increased since the last bid, see here.