Reddit:

• forces users to use a proprietary app full of trackers to collect data and sell it to advertisers
• blocks VPN usage

Lemmy/Piefed:

• browser access is encouraged,
• lots of third party apps, most of them being open source
• allows VPN usage

Privacy is a spectrum. There’s always a level of privacy you’re going to give away when posting or interacting on an Internet forum.

The levels of privacy that Reddit and Lemmy/PieFed offer are vastly different, for reasons stated above. Saying that they are not private is just going to deter potential new joiners to give them a try.