Perhaps you have misunderstood the purpose of marking a post with the Solution tag. It helps other users by identifying which topics have arrived at a satisfactory conclusion. The Solution post identifies the root cause and presents a means to resolve it.
It’s a handy aid when searching for answers to questions and is a suggested practice in the community guidelines document called: How to help us help you (see #21).
Many users overlook to perform this final step and I remind them to do so. On some occasions, they have marked my post and I have asked them to remove it and mark another person’s post because it was either first or better (or both).
To be clear, I only ask users to follow the community’s customs and never pressure them; ultimately, it’s their decision.
What is a regrettable practice is when the topic’s author copies someone else’s suggestion and then marks their own post as the Solution. They add nothing and only demonstrate their ability to duplicate a post. If I see someone repeat this behavior, I’m less motivated to provide them with assistance (because they can’t follow a simple community practice).