I like to think of Cloudflare like insurance. Any single website may need it rarely if ever, but if it happens to you, you have little to no recourse that doesn't involve large sums of money.

Instead, you pay Cloudflare a regular, small amount of money† to reduce the risk of having to pay a large sum of money in case you're targeted. This sounds almost exactly like insurance to me.

† Sometimes the marginal cost is actually $0!