I cannot find any real reason why you should spend your bitcoins in order to shop online.
In my opinion, Bitcoin has a bigger value than the one right now so it is not worthy spending them for shopping. It is better to keep them in your wallet and consider it as your investment. If you want to buy something online use a stablecoin...
Why not? as an investor, we can also spend, we can do both actually, so it's not wasting your bitcoin because as an investor, you'll ensure that you will not touch your investment until a certain time will arrive or it will hit your target.
If you have fiat now and you like to shop online using bitcoin, then you covert it, that's what people do, if they spend bitcoin it doesn't mean they don't value it now and its future.