I think they mean: there is no USB socket on the enclosure containing the AC-DC conversion circuitry, like you'd find on most smartphone charger bricks. The cable (with the USB-C plug on the other end) is attached to the enclosure permanently. Thus, when the plug breaks, you need to throw away the entire power conversion brick. If the converter had a USB socket, not only could you replace the cord when the cord inevitably breaks, you can choose the cord length and whether it has a 90 degree bend and/or magnetic disconnect at the end.

We have probably 10 Thinkpads at the house. Three power bricks have been rendered useless (and four USB-C ports) because Lenovo has set their part selection and engineering design to "best value for the company" rather than "best quality for the end user".

Also, the PD negotiation of the Lenovo bricks is unusual, where it will not provide significant current at the 5 volt base USB power to some non-laptop devices and also not accept fast charging rates from some non-Lenovo chargers: Our ThinkPads will charge using some high-wattage smartphone chargers but not every one of them. Every once in a while we find a device with a USB-C charging port (e.g. baby monitor display) that will charge with any charger around the house but not with the Lenovo laptop charger.

The "small ones" do. The larger P models require a beefy 220W proprietary power supply.