Why isn't there a button in the formatting options to add spoilers? Please do so as it would be helpful. (I know to manually add ! marks to blockquotes, but it can be tedious.)
If there is a button and I have missed it, sorry for wasting your time.
We don't currently have a button on any site to do spoiler formatting. The best candidates for that feature might very well be Movies & TV or Science Fiction & Fantasy. However, there has been some resistance to the very use of spoiler markup on those sites. See, for instance, "Are we overusing the spoiler markup?" The practice of editing out spoilers in titles has also met resistance.
Even on this site, where the purpose of many questions is to hide information so that other people can discover it on their own, spoiler markup has been overused. If you have a concluding sentence in your answer, a spoiler block might be smart to add:
Therefore the only person who could have done it is the butler.
But when your entire answer is a spoiler, that's a sign you might need to add more commentary. Ideally answers would look more like someone working out a Fermi problem and less like Final Jeopardy. (Part of the problem here, of course, is questions that can be answered in a single line.)
So, I don't think making it easier to create spoiler text, especially spoiler paragraphs is a good idea.