It is an excellent feature and something consumers crave knowing they can curb fraud. Many companies are now doing this. Capital One has the lock card feature, Discover has the Freeze it feature among others and hopefully their video convinces you as to why it is a good feature. https://www.youtube.com/watch?v=Z0ZNAHZlkMY
Seems like a useful feature to me.
While true, I locked my Simple card after a $20ish charge in the Dominican Republic, then initiated a support request asking about it. Simple's nice and refunds all fraud, but some banks I'd have saved $30 there.
Plus, your not being liable doesn't mean you don't pay for it. We just pay indirectly - it's figured into the bank's fees, the interest rates they'll pay you on savings, etc. I like Simple, and I was happy to be able to stop it myself before they went and charged $1k somewhere else.
And I know some people who have cards for online purchases only, which they use very rarely. Leaving the card locked except when actually in use would be quite a security improvement.