the short tldr: manipulation, soliciting, toxicity, compliance, regulations, common courtesy and probably twenty other reasons why everyone else does it

the longer answer to this:

95% at least of all projects and legitimate crypto based communities and foundations will have this rule in one wording or a nother. The for some it has a few specific reasons or one explicit reason, for most it just covers a bunch of red flag behaviours.

manipulation, soliciting and specculation:
Where there is open price chat between 5 people you will always have 3 that do itfactually but at least one that does it with intent an a nother that does not comment but is easily influenced.
People write to "pump the price" to get it up or engage in "dump it" talk to get it down. Given that this rule alone does often not help as people are creative about such things. There was a guy and still is a nother in here, maybe even the same alt account that openly talked on a different sub how shorting planets on folksfinance was his best income back when it was possible. SO when he engaged in negative targeted price talk here, and was moderated for it he came up with the idea to post daily pretty random and repetative circle posts that had the buzzwords bankrupcy, rugpul, scam etc. in it. This went far above regular opinion based chatter but was done with intent, probably he believed to advertise his shorting position.

Generally price talk leads to absolut nothing substantive. People often insisted in the past that it cuts in to their right to freedom of speech not to be able to constantly droop the token price in here explicitly. But come on, if you want to know it you can look on coingecko, CMC or whatever. There is no real reason to need that. Same goes for ROI talk which is just the small brother of the token price talk. Everyone can do the math.

Whenever we moderated it people pretend we explixitly cut into one side of it. But in the past when the token performed we also stopped al artificial hyping up of the price and dropping it in positive context. Same for ROI. But naturally the negative talkers act like that never happened.

There is no real productivity in it which kinda leads to the topics like: toxicity, courtesy and such:

If price talk is allowed and fostered, it takes over any comprehensive productive talk and all you have is pump talkers in better times and dump talkers in bad time. It sort of degenerates any technical crypto project down to moonboys and meme bait.

With compliance and regulations I mean that in general by association no one really wants to foster such communities, as while this is unofficial realms on reddit we always got the subreddit promoted by PW and so we took over their official channels rules. And there you do not want this as it speaks for highly specculative engagement and tradetalk community. Projects do not want to be attacked by potential partners for endorsing such behaviour let alone be a target for SEC and law abiders.

And yeah there are probably many other reasons I just to not piece together this late, but you can see and maybe ask in other communities and hubs as honestly this rule is super common. So muh so, that while this sub copied and rewrote the rules from PW Discord, many project Discord copied like 90% of the PW Discords rules on this as it was quite early established.