The drop is likely because inflation dropped, also looking at actual percentage numbers it looks like the popularity of euros already was low and dropped only slightly (e.g. ~35% -> ~30%)
Part of the experience that makes visiting countries with a different currency awesome is that you have no idea what the actual worth is of your spending. Euro is convenient though
You jest, and generally you're right, but my experience looking at my bank account after staying in Poland for a week was "wow, I only spent how much???"
The cost of living where I live has risen dramatically since the global financial crisis, but wages have stayed the same.
The usefulness of a shared currency has significantly decreased with the prevalence of digital banking and automatic conversion via bank cards. Meanwhile the 00's & '10s were a nasty lesson in what the liabilities of a shared currency are.