Recent Hack Attempts

I have several sites which have in the last month, experienced several attempts each day of attempts to login from all over the world and different IP’s.
I realize there may be someone using a VPN?
I do not allow registration on my website so it must be an attempt to create some mischief.?
Or is it?
Anyone who attempts to login gets five tries and if exceeded they are locked out for five days.
This doesn’t matter if they’re using a VPN which they can switch easily.
I have set the locked out message to send me an email if they have a question and are not trying to act my site but have received no replies.
Opinions and suggestions please?