Quite so! When I edit fiction or creative nonfiction for Prism & Pen, bad dialogue punctuation and wrong dialogue tagging are very common. I don't mind so much when British and British-style writers like Australians and South Africans put commas on the other side of quotation marks. That's correct for them and I'm content to either edit for standardization or just accept the authenticity of the difference.
But that period (full stop) at the end of a quote when the sentence continues? It's like nails on a chalkboard for me, and a sign that whoever wrote the sentence doesn't read enough books to know better.
Still, I try my damndest to be patient and helpful. I'd be a wealthy man if I had a dollar for every mis-punctuated line of dialogue I've fixed over the years.
So I thank you for manning (womaning) the grammar ramparts. Maybe if enough of us write about how to construct dialogue, amateur writers will finally figure it out.
Though I'm not betting any real money on it!