Sometimes I screen cap a picture that looks great in 16:9 PowerPoint and when I paste and save it in Snagit, then import into PPTX it gets blurry (imagine wants to save a great slide as a picture in PPT)
What does it look like in SnagIt? Acceptable quality I suppose. What image format are you saving in? Personally, I like to use PNG format. If you were to save in perhaps GIF format, you only have a limited number of colors available. Have you tried copying from SnagIt and pasting into PPT?