Fix and Flip as a practice predates the term itself. The concept has been around for a long time, going back to American Colonial times and even in England before American settlement. During this time, it was largely limited due to time and money constraints.
Also at this time, “Hard Money” loans are created and used to buy homes at a reduced price. These loans are largely from private lenders (usually real estate investors) with higher interest rates, lower loan to value (LTV), and are based on the home as an asset (not credit or proof of income).
In today’s world, the average age of homes in the U.S. is 36 years. With the concept of "Remodel & Sale" having been rebranded as "Fix & Flip", a subset funding industry was carved out to support increased American interest.