Shouldn't it be ETL (extract, transform, load) [1]?
[1] https://en.wikipedia.org/wiki/Extract%2C_transform%2C_load
[1] https://en.wikipedia.org/wiki/Extract%2C_transform%2C_load
In the old approach, you would run the transform BEFORE loading data into the warehouse. The disadvantage of that approach is that you loose all fidelity of the raw data.
In the new approach (Airbyte's approach), you load the raw data into the warehouse, and then run your transform jobs in the warehouse. You can do that because modern warehouses are cheap and scalable. The benefit of that approach is that you keep your raw data with all its fidelity, opening up endless opportunities for exploratory slicing and dicing.
That's why it's called "ELT" (new) these days, to distinguish from "ELT" (old).