Mandatory reviews will never happen, nor should they. We exchange our services for money. That is the extent of the agreement. A review is a privilege, not a right.
Many buyers do not want to leave reviews because they do not want what they buy to be public knowledge. About 50-70% (from my experience) of Fiverr buyers leave reviews - that is an amazing number compared to many other marketplaces.
Do you review every product you purchase on Amazon? Reviews are extremely important for Amazon sellers as well. Should they be mandatory? What about Yelp reviews for restaurants?
You should be happy that your customer complimented you. That means they liked the work. Many buyers do not even say thanks. They just download the work and use it without a word.
And, honestly, you seem incredibly entitled complaining about why your buyer would bother complimenting you without leaving a review. That is a horrible attitude to have
No, you cannot. Please stop spreading this nonsense. You will get a warning or a suspension if you do this. It is also very unprofessional.