Animal Crossing is a big system seller and brings new market tier. The growth of Xbox and PS4 is not the same, in size or shape. With Animal Crossing, switch have new type of consumers, because of that, the sales have big grow, second motive is Covid.
Individual games rarely produce long-term increases to baseline sales. That goes for the latest Animal Crossing as well. In Japan, where AC:NH is one of the most successful games ever and appears to be the biggest system-seller for any system ever, the effect on sales was short-lived. Sure, it produced one of the best sales weeks for any system ever in Japan (and the biggest outside of the December holidays or launch weeks), but just three weeks later sales were back down to baseline levels, with said baseline not appearing any higher than the previous baseline. Even in the U.S., I can't seem to find a single instance of any individual game released in the past three generations producing any detectable gains for a period lasting more than two monthly sales periods (and in some cases those gains may have been assisted by other factors like price cuts). Usually you just see a spike in sales the month the game is released (and since U.S. sales are tracked monthly instead of weekly like in Japan, it takes a particularly big system-seller to make itself obvious in the data).
As for the PS4 & XBO, of course their COVID boosts haven't been as big, because they're old systems nearing the ends of their lives (five months to go until replacement). While demand was temporarily up as people got their stimulus checks, overall demand is down so sales may not be as high in absolute terms as they could have been if they were close to their peaks. Also, the total number of systems in the supply channel isn't going to be as big as it once was because shipments decline in late life, so there is likely less supply to meet the recent increase in demand. Even then, though, this past April was the second-biggest non-holiday month ever for the PS4, and tied with October 2016 (One S launch month) for biggest non-holiday month ever for the XBO. The PS4 and XBO were up 178% and 210%, respectively, from April 2019. Not as big as the Switch's 256%, but still massive.
Now, for March the Switch was up 161% from February, while for the PS4 and XBO their gains were 79% and 70%, respectively (March is usually down from February barring other factors). That's a much larger disparity than for April, which is where we are likely seeing an effect from AC:NH, but the smaller proportional gap in April suggests the AC effect wearing off. For May, the PS4 and XBO were down -62% and -54% from April, respectively, while the Switch was down only 34%, but with us being this far out from AC's release, I'd say it's more likely that we're seeing the effects of stock come into play after weeks of artificially increased demand for consoles.
Given the typical short-term effects of system-sellers as well as the observed effects of COVID-19 and the resulting windfalls from stimulus, the vast majority of the Switch's gains can be attributed to that, and not to Animal Crossing. There is no reason to assume that AC will by itself be capable of enhancing Switch sales for a long period of time. It didn't do so in Japan, and, especially given the external factors at play, there's no reason to think the situation is any different in the U.S.