For all its warts, C++ only got adopted inside AT&T and later by almost every C compiler vendor, because it just fitted on their existing toolchains.

Even lack of modules is related to that, C++ object files needed to look just like C ones.

Now that C++ is grown up and can live on its own, it needs to pay for the crazy days of its parties going out with C. :)

State of the art or flavor of the month? For instance, the features from functional programming that C++ and Java recently (in the last decade) added weren't anything new. When functional programming started to become more popular was when their features started showing up in C++ and Java.

If people are concerned that your language is already to large than adding elements from other programming paradigms because they're suddenly what's hot doesn't seem like a great idea. It feels like some languages are chasing the crowd, which can lead to a messy language ("OOP is all the rage now? Our language is all about OOP! Oh, functional is all the rage now? Well, we just nailed on some functional features!").

It's also true that it may not be necessary.

What makes a good language? One that randomly accumulates state of the art ideas about programming without breaking old code, or one that gets out of the way and allows requirements to be expressed reliably and relatively simply?

Of course C++ is used because it's fast. It's fine in limited domains like DSP.

But what is the rationale for a language that whimsically accumulates new features every couple of years, while failing to deal with basic challenges like memory management?

It's not as if it's ever going to reach a critical mass and turn into Haskell.