I think this is a particularly rose-tinted glasses view of the sales process, which sells underquoting as a great thing for your customers that they will love ('When you tell them they need to pay more, they will love you and will recommend you to others!'). In reality, 'land and expand' is almost universally hated by customers and this just appears like an excuse to under-quote to win the commercial point on an RFP…
I have never seen anything remotely to your ideal. Did you forget how competitive and cut throat the world is? You don't sell, you don't eat. Sales is a race to the bottom, a competitor will eat you alive by undercutting or over-promising just the right amount to win the deal.
I'm in the UK, and USA providers are more 'cut-throat' than domestic UK providers in my personal experience when I have tendered enterprise software in the past, and the cultural differences have been massive.
Cut-throat is fine until you get a reputation for cost overruns, get to be known as untrustworthy, and eventually end up with a lack of customers willing to give you positive references. I certainly know which vendors in my industry are known for land & expand and scummy sales tactics (and when I personally see these tactics being deployed I will tell everyone else I know in the industry to avoid them like the plague).