Why is SMS CAPTCHA not humanized?

I found that the mobile phone CAPTCHA sent when registering on the Internet is usually a 4-digit, 6-digit pure digital verification. But this kind of user experience is not good, if it is very long and easy to type wrong, it is usually a random number between 1111 and 999999. Why not design it into three. Or a number that is easier to enter with a hyphen?

CAPTCHA python
Mar.05,2021

this is also an indirect default standard, too little (too little is possible to try to get the right number), too much is not good, 4-6 is the best, 6-digit is the best, you see Alipay, WeChat Pay 6-digit, bank card password 6-digit

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bdf589-31467.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bdf589-31467.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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