This is known as "E notation," it is common in calculators with limited character sets and was popularized by the languages C and Fortran.
I don't think E notation is a great default because it is not universally recognized by the standard libraries of all major programming languages. Suppose I write a program foo
(in Rust) which prints floats to stdout, and my colleague (unfamiliar with Rust) writes a program bar
which parses floats from stdin. If their language does not have built-in for support parsing numbers of the form 1e3
then my colleague needs to bring in a dependency or write their own floating point parser.