We frequently judge old technology unfairly because we do not account for the user or technical environment at the time. Classic BASIC is considered a "bad" programming language because it has line numbers, no local variables, spotty support for user defined functions, no user defined data structures and largely implementation specific I/O.
What we forget is BASIC was designed for mainframe systems of the 1960s. And its original objective was to teach programming to "non mathematical" users (not to write commercial software.)
If you wanted to write code on a classic 8-bit micro, your primary choices were: assembly language, FORTH, BASIC or UCSD Pascal. And Pascal might not have really counted because it required SO MUCH MEMORY! (I think it required 48k of RAM on the Apple II.) FORTH was a capable language, but it's stack-based reverse-polish syntax confused more than a few people. As an industry we wanted to make computers seem as user friendly as possible, and telling people they had to write programs in assembly language would fail miserably at this goal.
So this left BASIC. And had it not been BASIC, it would have been some other language like BASIC: byte-code interpreted, limited or no local variables, limited or no data structures, etc.
But the most important feature of early 8-bit micros is they booted into BASIC. You turned on the machine and in a few seconds, you got the welcoming "READY" prompt. There was no command line or shell, there was a programming language. And it usually booted pretty fast, within five seconds of turning on the power. You went from "off" to "programming" in five seconds or less.
Neal Stephenson once wrote "In the Beginning was the Command Line," and that's probably true for mini-computers, but for micros, the command line came after we were ejected from the algorithmic Eden of the BASIC interpreter.
Modern audiences might find it odd to boot a computer into a programming language (and a programming language with as many limitations as BASIC.) But at the time it seemed natural. What do computers do? They compute. How do we tell them what to compute? With programs! And micro-computer vendors of the late '70s believed their systems would be programmed by the same people who bought the system.
This sort of made sense in the 1970s. Apart from a few applications where micro-computers replaced complex logic assemblies in manufacturing and scientific applications, they started as hobbyist curiosities. Early adopters (like myself) immediately saw some application in their personal lives. I used a computer to calculate where I should point a telescope for maximal enjoyment of Messier objects. A friend used his Apple II to control a series of spinning prisms and replicated the laser light shows he had seen at the local planetarium.
Micro-computer business tycoons (Steve Jobs being the most obvious) figured out corporate early adopters were using micros to dis-intermediate corporate data processing groups. Booting systems into BASIC let these corporate pioneers start quick with the business of thumbing their nose at the corporate data processing groups who often charged obscene amounts of "internal corporate funny-money" to sort a data set or perform simple calculations. In the late 1970s you didn't have a computer to play Mario-Cart or send email. You had a computer to solve one or two specific real-world problems or maybe you were a geek who liked to play with technology (or both.)
VisiCalc would eventually come along in '79 and kick-start the commercial Independent Software Vendor (ISV) market for small computers. But even VisiCalc was a programming language of sorts; just one with a highly constrained user interface. But it took another five years or so for the "Boot to BASIC" concept to eventually die off. By that time 16 and 32 bit systems were starting to gain traction in the market. The Macintosh demonstrated what a computer could be (though it was still horribly expensive.) Jack Tramiel's 8-bit commodore line lasted throughout the '80s as the "computer for the masses, not the classes." If you didn't have the cash for a Macintosh, Amiga or Atari 520ST, you could always pick up a C64 dirt cheap.
And when you turned it on, you would see:
**** COMMODORE 64 BASIC V2 **** 64K RAM SYSTEM 38911 BASIC BYTES FREE READY.
And you couldn't do much compared to today's machines, but what you did was all yours, baby!