ISP. Your provider is able to view everything you transmit over the Internet in unencrypted form, and also sees where and when you connect. That's why it's worth using a VPN!
Third party applications. Any apps you install on your device can have access not only to your traffic, but also to the data of other apps you run. All of this can be used to display annoying targeted ads.
VPN Providers. Most VPN services (not us!) transfer your personal data to third parties for commercial purposes! For them, this is a way to make good money
Intruders. Various types of network attacks can be carried out on a segment of your network. Do not allow Internet attackers to determine your IP.
Corporations. They know all about you. VPN is not an option if you are integrated into their infrastructure using enclosed systems.