1) The base configuration comes with insufficient resources (low memory, low disk space, till surprisingly recent past slow HDD instead of SSD), and
2) The upgrades are way too expensive compared to any other hardware manufacturer, meaning that
3) The advertised price is a lie! Almost no one should buy the base configuration.
You see a device advertised as 1500$. You think "Sweet! That's the price I am willing to pay!". But then you go through the selection process and end up with a 2000$ minimum on the checkout page. Even though it's not the same, psychologically, it feels like when you try to get an AirBnB for 100$ a night for 3 night and end up seeing a price of 920$ in the checkout page instead of 300$.
Apple is pricing necessities (like 16 GB of RAM) as luxuries, and people don't like that.