As I have previously said, not everyone can or want to spend money buying the most expensive storage configuration at the time of initial purchase.
For example, the retail price for the MacBook Pro 15-inch (non dGPU) with 256 GB SSD is $1999. The upfront cost of upgrading to 1TB SSD is an additional $800 and many people cannot or do not want to spend another $800 upfront.
Perhaps you are fortunate enough to be able to easily spend another $800 at the time of purchase, but that is not the case with many others.
What "mistakes" did I made?
Also, how am I being "dishonest"?
You have said it many times and we all agree not everyone can afford to buy a Mac specced as they want at the time of purchase.
However we seem to diagree on the solution. The solution is don't buy one then, all this "how can I do it on the cheap, risking voiding warranties, having to put bits back in for service or repair," it can all be avoided (as can all this pointless banter) by buying a cheaper computer with the specs or upgradeability you want from another manufacturer. Problem solved.