Alan Kay, one of the lead developers of Smalltalk, said it was also valued for being good for bootstrapping ideas for building systems. He went into that topic starting at 58:50 in this talk:

Alan Kay at OOPSLA 1997 - The computer revolution hasn’t happened yet https://www.youtube.com/watch?v=oKg1hTOQXoY&t=3530s

“To me the most distressing thing that happened to Smalltalk when it came out of Xerox PARC was for many respects and purposes it quit changing. Now I can tell you at Xerox PARC there were four major versions, completely different versions, of the language over about a ten year period. And many dozens and dozens of significant releases within those different versions. And I think one of the things we liked most about Smalltalk was not what it could do but the fact that it was such a good vehicle for bootstrapping the next set of ideas we had about how to do systems building. And that for all intents and purposes when Smalltalk went commercial ceased. Even though there was a book, the famous blue book, that Adele and Dave wrote that had the actual code in it for making Smalltalk interpreters and starting this process oneself, almost nobody took advantage of this. Almost no university took advantage of it, almost no commercial institution took advantage of it. And what they missed was, to me, the deepest thing I would like to communicate to you today, and that is we don’t know how to design systems yet. So let’s not make what we don’t know into a religion for God’s sake. What we need to do is to constantly think and think and think about what’s important. And we have to have our systems let us get to the next levels of abstraction as we come to them. And the thing that I’m most proud of about Smalltalk, pretty much the only thing from my standpoint that I’m proud of, is that it has been so good at getting rid of previous versions of itself until it came out into this world. Now one of the reasons we got involved in doing Smalltalk talk again, for me it was after 16 years of not working on programming languages, a couple of years ago we started this project we called Squeak, which is simply, not an attempt to give the world a free Smalltalk, but an attempt to give the world a bootstrapping mechanism for something much better than Smalltalk. And when you fool around with Squeak please please think of it from that stand...think of how you can obsolete the damn thing by using its own mechanisms for getting the next version of itself.”

The original Smalltalk-72 focused on teaching children, but for Smalltalk-76 Alan Kay and Dan Ingalls wanted different things. Alan wanted to continue the kid focus while Dan argued that a language focused on advanced programmers could be used to implement a children's language on top of it. He was proven right decades later when EToys and then Scratch were implemented on top of Squeak Smalltalk, which closely followed Smalltalk-76.

This confusion frustrated me when I first read about Smalltalk in the August 1981 issue of Byte magazine. I couldn't figure it out and at that point I had learned several programming languages and none of them took me more than two hours to become reasonably fluent in. So I was having problems with a language that kids were using?!? Later on I found out about the differences between Smalltalk-72 and -80 and that the Byte articles explained things that made sense if you already knew them but didn't help you learn in the first place. All variations of Smalltalk have become my favorite way to program ever since.

Also, even though it called itself purely object-oriented, the earlier versions lacked inheritance.

Nowadays object oriented programming is almost entirely associated with inheritance hierarchies.

Perhaps inheritance isn't as central to object oriented programming as initially envisioned.