Reliable at what, pulling the unit off the shelf when the cable is tugged? Making you spend more money to replace the whole unit when the cable is damaged by kids/dogs/cats? The benefits far outweigh the costs to supplying it with a detachable cable.
It seems you are not familiar with the word reliability.
And from what you posted you must have a lot of stories to tell about all of the power cables you have damaged from being careless, having kids/pets etc. I'd enjoy hearing a handful.
Me? None. I have integrated power cords on loads of devices and tools in my woodshop. Toasters, floor lamps, coffee-makers, rice cooker, hair dryers, desk lamps, sawz-all, paper shredders, heat gun soldering iron, Dremel tools, drill, audio gear, TVs, five HomePods, wood planer, wood routers, jigsaws, Fein detail sander, miter saw, air compressor, grinders, Festool track saws and sanders, other circular saws, three portable shop vacuums, rotary hammer, radios, portable shop lights, woodworking tools battery chargers, and on and on, and on. And an electronic lab with test equipment. Over many many years and with pets. With frequent and often rough usage.
I have NEVER had to deal with a faulty integrated power cord. Not once!
Fretting over HomePod Mini having an integrated power cord is a BS issue.