Hi Natali,
This is indeed something that Marketo has done, quote from Erik (Marketo Employee):
"We did this deliberately. There were some inconsistencies in how we did the link tracking for tests, and we took the opportunity to remove them alltogether.
Should you want to test out the link decoration for tracking, you can send the email via a Single Flow Action or test campaign.
Glad it helps your testing!"
-Caleb