Although I do understand that, it might have seemed more consistent to also make eval { } compound?

eval EXPR is often used more like a function ($sum = eval("3+4");), and the return value of eval BLOCK is important too (e.g. Bug in eval in pre-5.14). Thus it is consistent with e.g. do BLOCK, map BLOCK, grep BLOCK, and less with if, which though it has a "return value", I've very rarely seen it used, and e.g. the return value of for should explicitly not be relied upon (I can't find the reference for the latter right now but that's the gist of it). Think of eval like a function with a special syntax for its argument and it makes sense.