True, but you can create something almost like a hardware wallet with Mycelium. Take an Android smartphone. It can be one that is just barely capable of running Mycelium, because the idea is to run nothing or very little else on it.

Install Mycelium, then safeguard the phone. Lock it down. Do not install anything else on it that could possibly reduce your security. For example, take an older, but sufficient phone, install CyanogenMod on it, but not the Google apps. Now you have a minimalistic phone that does not even have the Google Play Store and has no connection to Google whatsoever.

Install Mycelium on it (by copying the APK file to the phone and installing it). Now, as long as you keep it safeguarded and inaccessible, you have something that is much more secure than any ordinary smartphone. True, it is not really a hardware wallet, but it comes fairly close.

Also read up on the true hardware wallets that work with Mycelium. I like my Trezor, for example, but there are at least two more hardware wallet types that work with Mycelium and that can keep even large bitcoin amounts safe while still allowing transactions with them.