The advertisements are turned ON for your lock screen by default, which is definitely a clever way to offer companies to reach their customers, without mentioning the word 'advertisements' to the Windows users.
If you don't want to see these intrusive ads, follow the steps given below to disable Windows Spotlight:
- Open the Start Menu and look for 'Lock Screen Settings.'
- Under 'Background,' Choose either 'Picture' or 'Slideshow,' instead of Windows Spotlight.
- Now, Scroll down to 'Get fun facts, tips, tricks, and more on your lock screen' and uncheck this box.
Full article: Windows 10 Started Showing Ads on LockScreen