What could be wrong when editing sysctl.comf?

Question

linux

You need to configure the use of the swap partition.
I add the line to the /etc/sysctl.conf file
vm.swappiness=10
However, after a reboot sysctl vm.swappinessit returns 60, as it was before the reboot.
On prompts from the Internet, I tried to create the /etc/sysctl.d/99-swappiness.conf file
and write it there vm.swappiness=10
. Everything worked out.
Explain, please, who knows why? why is sysctl.conf not working?

Answer 1

cat sysctl.conf 
# sysctl settings are defined through files in
# /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/.
#
# Vendors settings live in /usr/lib/sysctl.d/.
# To override a whole file, create a new file with the same in
# /etc/sysctl.d/ and put new settings there. To override
# only specific settings, add a file with a lexically later
# name in /etc/sysctl.d/ and put new settings there.
#
# For more information, see sysctl.conf(5) and sysctl.d(5).