Raffzahn gave a fine, complete answer. Don't mean to compete with any fact or conclusion drawn in it.
As they say, "that said"... There's a little more.
Consider the layout of the arrow keys in the first pic. Well, second too, of course, but the earlier keyboard being more directly to the point as it is earlier in the evolution. Why would the keys be placed as so, up arrow the "8" and so on? Why not "1-2-3-5" (maybe some time traveller influencing something trivial for some fun) or "decimal point-1-3-5" to get a diamond shape that kinda feels pretty natural while the current "one over three" button array does not?
Not a technical expert here so no wonderful list of cool older computers from outside the micro-world will follow. But I did have plenty of experience using my employer's software grafting something of a POS onto a warehouse program and so using equipment in a mixed typing environment, one of numbers and letters with the numbers being a bit more important. Probably a mainframe in the back end as people called it so, but it could have been a mini-computer for all I know.
In any case, the "numberpad" was on the left side of the keyboard, not a physical numberpad, but sharing the QWERTY letter keys. And it was laid out the way the keys are on that first keyboard's (yes, and all 400 billion of them since) physical numberpad.
Anyone who used both navigation AND numberpad aspects, like me, was very used to this layout. It WAS awkward in that most were no more left-handed than I, and I imagine that's part of how it ended up on the right-hand side, not the left (piles of function keys being common on the left being a bigger element in that choice, I further imagine). But that layout, both of numbers and of navigation keys, might have been something they would have thought important to preserve as there was only a shift of hand with the burned in pattern the same.
IBM, in particular, was always a "you get precisely what you pay for... and not an jot more... even when you didn't realize how closely they could slice against that bone" kind of company. Putting extra physical keys on a keyboard costs incrementally more, the same way $5 more for the gas tank of a Ford Pinto would save lives but making a million of them that's $5 million and maybe the lawsuits would come to less so... They keys we have today, versus the 88 they had to start with, came only grudgingly.
Therefore I cannot say as a fact they thought deep in their bones that any numberpad put on the keyboard MUST, just MUST, include navigation ability as well to properly care for their incumbent computer users rather than just being cheap &%#$)'s who were HUGELY grudgingly seeing themselves forced to provide for a numberpad. But I will say it seems a very NATURAL evolutionary move. They were providing a numberpad, grudgingly or not, so why not be brilliant and bring navigation into the game? (Outside just Enter and TAB, that is.)
And one still needed to have a function-style key to do the switching back and forth. Probably was either innovative to have a dedicated key for that guessing it wouldn't be needed too frequently or perhaps just a techspec timeline running out and someone pointing out software folks were owning the function keys there were so maybe they couldn't really use them for it without trouble.
Hence the dedicated NumLock key.
(And believe it or not, ScrollLock was useful once upon a time, and I cry myself to sleep (metaphorically) about having no modern PauseBreak functionality.)
So I will say, for me the preponderance of guess-idence says that's what happened. And it wasn't enough so we got the modern one-over-three set of arrow keys. And the "Home-End-PageUp-PageDown" set as well.
If I am correct, that would be about the lowest level explanation of why they came into existence TOGETHER, not separately and later combined. (And usability would later separate them.) And which I think the poster would be happy to know of as a small point to go with
Slightly aside, that is also how some of the shortcuts we usually still have access to in software came into being as well. I loved WordStar when entered the PC world (and Locascript in the CP/M world... what that program got out of a dot matrix printer vs. what DOS got for years was incredible). It used a shortcut convention I do not know the name of, but that convention either came from the mainframe/minicomputer world or was powerfully influenced by it because it fit perfectly everything we had to do at that job. I loved WordStar for its functionality and the user's detailed control not for its chosen shortcut convention, but that was nice too. (And yes, my "user's detailed control" was, for 99.99% of people, "I hate it, it doesn't DO anything for you, you have to do every little thing." But you know, potato-pah-tah-toh.) Connection being the left side of the keyboard being used a lot of ways, not so much the right side, though it was also.
So I think someone with more knowledge or technical experience from the time could regress the layout and need for switching even further.