"This feels almost like a bug because we can copy and paste blocks into multiblock fields, which is awesome 
. Not having the ability to reuse a block in a single block field makes me hesitant to use it.
I think this feature isn’t available in single block fields because the paste action is located in the block’s kebab menu.
To improve this, the paste option could either be moved out of the kebab menu, or there could be options like ‘paste above,’ ‘paste below’ in multiblock fields, and a ‘replace block’ option in single block fields."