"The perfect is the enemy of the good" =/= "every system is so flawed you shouldn't even try." You're totally right that oddities here and there, whether raised by the quirks of a particular campaign or caused by simple design oversight, are probably unavoidable. Doesn't mean that it's totally pointless to have such information, for the people that want something to work from/adapt.
I agree that just because something is hard doesn't mean it shouldn't be attempted.
But they did attempt something. It's in the book. The problem is that what they did wasn't "good enough" for many.
If you're referring less to having magic item crafting and pricing and more having individual prices, it gets more complicated. I think time was also a factor, as the book was already late. Evaluating every item and fitting it into one of three categories is quick. Coming up with a individual price for each item and then comparing that to every other related item is much more time consuming.
A fan did this, and their work is linked elsewhere in this thread. It took them six months. Now, assuming they only spent an hour or two each day on the project, a couple dedicated writers focusing on that task for half of each workday could hammer that out in... a month and a half. I don't know how the fans would have reacted to the DMG being delayed until February for magic item pricing.
There's also the inflexibility of set pricing. It makes it harder to adjust the price since the default assumption, what is given in the book, is that Magic Item X costs "### gp". And varying from that, even if doing so is encouraged in the book, is a house rule. It's not as adaptive to customization.
And that's not considering the problems with setting a fair, absolute price for all magic items. Because magic can vary so much by situation. My favorite example is
winged boots versus
slippers of spider climb. Right now they're ostensibly the same price as both are uncommon. But if setting a firm price for each item most people would place the slippers below the boots because flying is seen as more powerful. However, going with the
Princes of the Apocalypse adventure, at least 75% of the encounters in that adventure take place in small dungeon chambers where elevation means little. There's no functional advantage between flying near the ceiling versus climbing on the ceiling. Except someone spiderclimbing won't fall if knocked prone and the slippers function continually. So they're arguably far superior.
Which is the problem. The value of items doesn't just vary from campaign to campaign but from adventure to adventure and even encounter to encounter. An absolute price is arguably impossible. There are too many variables.
The only way around the number of variables is to assume a standard mode of play. However, there really isn't a single common playstyle. The surveys reportedly showed that. So it'd really be picking the largest majority or the preferences of the designer and codifying around that. Which may be somewhat unsatisfying for the majority of players. And makes the rules a trap for those new to the system who are unaware that prices are based on a playstyle they might not share.
The first point means that nobody in the group has a special attachment to it, so they're going to be more likely to evaluate it objectively, or at least subjective to what it does for them, rather than subjective to what it means to them (e.g. it's nobody's "baby").
This is true in theory, but gamers are nothing if not critical and argumentative. This thread alone proves we're not very objective at evaluating a magical system, even one not created by us.
The second point means that there is less--not zero, but less--potential for unexpected "gotcha" ideas; everyone had to learn the system to the same degree, and from the same source. If there's a conflict of understanding, it can be addressed by reviewing the text and pointing out the places where one got the ideas one has, rather than having nothing but one's own mind to point to.
This can be solved by printing out house rules and codifying the system. But, in the event of conflict, it's still typically going to be addressed by the DM's opinions and preferences, regardless if it's written down or not.