What is reason for fixed system data format?

[Alex Keda]

I looks means for global change system date format (example -> 
2007-07-07 21:48:58). But - it not exist.
In code some applications I see fixed string for length date string 
(example - ./usr.sbin/syslogd/syslogd.c).
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What reason for use fixed format, and is exists plans for change this?