It's not a problem, it's a solution (against resulting problems if more characters would be alowed).
The significance about 63.DOMAINS is their combination of their pattern in the maximum number of characteres and their TLD.
If those points fitting perfectly together, then they are perfect 63.DOMAINS which are highest in it's exclusivity, highest in it's demand and highest in it's pricing.
An extremeley rich person (contemporary art collector, enduser) who can buy any domain he want, wouldn't buy 'just a boring 1 character domain'.
He would buy the highest of all 63.DOMAINS - the one, which is a combination of an untoppable pattern in the maximum number of characteres and an untoppable TLD - in other words, he would buy
โ
THE MOST EXPENSIVE DOMAIN OF ALL TIME
toptoptoptoptoptoptoptoptoptoptoptoptoptoptoptoptoptoptoptoptop.top
21 times top / TLD .top
21 x 3 charachteres = 63 characters
63 characters + TLD .top
The highest possible combination, true perfection.
That's what I think what every billionair would prefer.
In front of this domain every 1 character domain is a 'joke'.
That's how I see it.