C# accidentally solved this problem with extension methods, these little helper utils at least get grouped by type and not in one humongous file. Or maybe that was part of the design team's intention behind them all along.

And because they're static you can easily see when services or state are getting passed into a method, clearly showing when it should in fact be some sort of service or a new type.

Even in architectures that start as distributed, I’ve seen the “involuntary monolith” arising.

Way too common, unfortunately.