8.0 puts models in app/Models by default, and an existing project can move them or not — but the reason to move is not the convention.
$ ls app/
Console/ Exceptions/ Http/ Providers/
Order.php Customer.php Product.php Invoice.php ← 41 of these
$ mkdir app/Models && git mv app/*.php app/Models/
$ find . -name '*.php' -exec sed -i 's/App\Order/App\Models\Order/g' {} +
# and the generators find them automatically afterwards
Forty-one files at the top level of app/ next to four directories is a listing nobody can scan, and that is the actual argument. The move is mechanical and touches every import, so it belongs in its own commit with nothing else in it. Laravel checks for the directory and adjusts its generators, so no configuration changes — which is the detail that makes this a five-minute job rather than a migration.