From a game design standpoint, starting at level 1 (or possibly 2 or 3) makes a lot of sense. You start out without a lot of decisions while you're learning the basic mechanics of the game. As you level up (quickly, at first), you get to make choices about how you grow and add more abilities/spells depending on your choices. It's easy to understand these new abilities and spells because you're learning one or two at a time. The tools are simple, but that doesn't mean that they aren't interesting.
On the other hand, if you're starting at e.g. level 7, you have to make a ton of decisions right out of the gate, before you even understand how to play the game. A level 7 wizard has to choose 4 cantrips and 12 spells and an arcane tradition without having a good way to evaluate the differences between them. You can have defaults, but that doesn't help you when combat comes around and you have to choose between spells and cantrips or understand how spell slots work and why you might choose to upcast.
I get that people want to feel powerful. Folks who already know D&D and/or RPG video games (and these forums certainly select for that, by their nature) might feel comfortable bypassing that early learning. But when we hit release and the player base gets much wider, a lot of people are going to get frustrated and overwhelmed when you throw them in the deep end with a ton of options and insufficient experience to weigh those options.
