The price of BTC went up by $2k USD in 2 hours this morning. Why would anyone want to use it to buy something when there's a good chance it'll be worth more in a day or so?
And conversely, it just fell by $3,000 in 20 minutes. Why would anyone accept it for a purchase when there's a good chance it'll be worth substantially less not long after?
I think that is their point. It would be nice if BTC would stabilize so that it can actually be used for purchasing something other than USD.
Keep in mind, the change in $ isn't important, it's the percentage change over time and the variance.