Ubuntu 22.04: file time info is missing for some of them

Code:ls -lt /var/log/
total 8628
-rw-r----- 1 root adm 97601 Dec 23 2023 dmesg
-rw------- 1 root root 2164 Dec 23 2023 boot.log
drwxr-x--- 2 mysql adm 4096 Dec 23 2023 mysql
-rw------- 1 root root 39013 Dec 23 2023 boot.log.1
drwxr-xr-x 2 root root 4096 Dec 23 2023 atop
-rw-r--r-- 1 root root 2275 Dec 23 2023 gpu-manager.log
-rw-r----- 1 syslog adm 305734 Dec 23 09:13 kern.log
-rw-r----- 1 syslog adm 1844481 Dec 23 09:13 syslog
-rw-r----- 1 syslog adm 44518 Dec 23 09:13 ufw.log
-rw-r----- 1 syslog adm 13712 Dec 23 09:09 auth.log
-rw-rw-r-- 1 root utmp 29952 Dec 23 08:55 wtmp
-rw-r--r-- 1 root root 56526 Dec 23 08:54 ubuntu-advantage.log
-rw-r--r-- 1 root root 2282 Dec 23 08:53 gpu-manager-switch.log
-rw-r--r-- 1 root root 112342 Dec 22 21:55 dpkg.logAnyone know please why ?