You don’t really need dedicated instructions for them. Programmers can do that today, and many decades in the past too, with software. For example, Java has Big

You don’t really need dedicated instructions for them. Programmers can do that today, and many decades in the past too, with software. For example, Java has BigInteger in the standard library for decades now. The reason they did not is less about memory (it would save memory on average, many numbers in that system need less than 4 bytes) more about CPU time. That system is likely very old, older than wide adoption of 64-bit processors. The reason we don’t often use variable-length integers now, memory and storage are cheap. For new software people simply use 64 or 128 bit integers. Still, variable-length integers are widely used when storage or bandwidth matters. They are all over binary network protocols, multimedia containers, and media codecs.