One, I'd argue that hits-based giving is a natural consequence of working through what using "high-quality evidence and careful reasoning to work out how to help others as much as possible" reallying means, since that statement doesn't say anything about excluding high-variance strategies. For example, many would say there's high-quality evidence about AI risk, lots of careful reasoning has been done to assess its impact on the long term future, and many have concluded that working on such things is likely to help others as much as possible, though we may not be able to measure that help for a long time and we may make mistakes.

Two, it's likely a strategic choice to not be in-your-face about high variance giving strategies since they are pretty weird to most people. EA orgs have chosen to develop a public brand that is broadly appealing and not controversial on the surface (even if EA ends up courting controversy anyway because of its consequences for opportunities we judge to be relatively less effective than others). The definitions of EA you point to seem in line with this.

First, I don't think that's the best "current" definition. More recently (2 years ago,) Will proposed the following: 
 

Effective altruism is:

(i) the use of evidence and careful reasoning to work out how to maximize the good with a given unit of resources, tentatively understanding ‘the good’ in impartial welfarist terms, and

(ii) the use of the findings from (i) to try to improve the world.

But Will said he's "making CEA’s definition a little more rigorous," rather than replacing it. I think the key reason to allow hits-based giving in both cases is the word "and" in the phrase "...evidence and careful reasoning." (Note that Will omits "high quality" from evidence, I'd suspect for the reason you suggested. I would argue that for a Bayesian, high-quality evidence doesn't require an RCT, but that's not the colloquial usage, so I agree Will's phrasing is less likely to mislead.)

And to be fair to the original definition, careful reasoning is exactly the justification for expected value thinking. Specifically, careful reasoning  leads to favoring making 20 "hits based" donations to high-risk-of-failure potential causes, where in expectation 10% of them end up with a cost per QALY of $5, and the others end up useless, rather than a single donation 20x as large to an organization we are nearly certain has a cost per QALY of $200. 

I think this excerpt from the Ben Todd on the core of effective altruism (80k podcast) sort of answers your question:

Ben Todd: Well yeah, just quickly on the definition, my definition didn’t have “Using evidence and reason” actually as part of the fundamental definition. I’m just saying we should seek the best ways of helping others through whatever means are best to find those things. And obviously, I’m pretty keen on using evidence and reason, but I wouldn’t foreground it.

Arden Koehler: If it turns out that we should consult a crystal ball in order to find out if that’s the best way, then we should do that?

Ben Todd: Yeah.

Arden Koehler: Okay. Yeah. So again, very abstract: whatever it is that turns out to be the best way of figuring out how to do the most good.

Ben Todd: Yeah. I mean, in general, you have this just big question of how narrow or broad to make the definition of effective altruism and it is a difficult thing to say.

I don't think this is an "official definition" (for example, endorsed by CEA) but I think (or atleast hope!) that CEA is working out a more complete definition for EA.