Do you know why? The drug he was posting about before that tweet, `chloroquine`, is already facing shortages around the globe for people already on it for non-COVID-19 treatments, including people suffering from Lupus [2].
He probably got attacked for promoting it in previous tweets, which is the likely context of the one you linked to, and is regardless a very valid concern for a popular figure tweeting about possible treatments. I've seen others telling people to be cautious promoting it, as we don't need people also needlessly hoarding a critical drug which is quickly becoming a frontline treatment for Coronavirus.
On the brighter side, France has a company promising to produce millions of doses:
> French manufacturer Sanofi has said it could hypothetically offer enough doses of Plaquenil - a drug containing the molecule hydroxychloroquine - to treat up to 300,000 people if necessary.
https://www.connexionfrance.com/French-news/French-lab-Sanof...
Not sure what the status is on other generic pharma companies who produce it. I know Teva produces chloroquine, but not hydroxychloroquine (Plaquenil) which is apparently "3x more effective" with coronavirus, and is mostly based in the US (NJ). I'm sure they've all been aware of this since February at a minimum when it first made the rounds as a possible treatment.
Well, we'd have to choose between telling the people with Lupus that, and telling the folks with SARS-CoV-2 the same thing, except even worse (because suppliers have not had a chance to react to that increased demand). Are we sure that the former is preferable?
It's available in many countries over the counter, so you can't be sure it will only be purchased with a predefined need.
Regarding that tweet, the only pass it was from March 6 (maybe, but probably not, best not to say anything early on). Even our Canadian gov spent the last month or so saying "there's no scientific evidence supporting border closure" [1], including in comments by our health minister a few days before they indeed closed all of Canada's borders. Nearly every person getting diagnosed w/ COVID-19 in Ontario has traveled recently, even the cases from today [2].
Nothing wrong with being wrong and later being educated on the seriousness - Elon seems to have changed his tune recently which is good. A concept that is frequently lost in our social media outrage machine. Not everyone is wise enough to not make public statements with such certainty, even our well-educated health ministers... meanwhile panic buying TP didn't do anyone any good either.
[1] https://www.thestar.com/politics/federal/2020/03/12/after-tr...
[2] https://www.ontario.ca/page/2019-novel-coronavirus#section-0 (note: how travel + country name is next to almost every case, even well into March 18th)
Drop the wall and you'll have your drugs in days. If you have 'backorders' for your Lupus patients, then you've already failed at something trivial to solve.