You're not wrong in saying that m7m=5,yescrypt=7 and m7m=5000,yescrypt=7000 will provide identical results. However, if your intention is for the stratum servers to ensure that you're always mining the most profitable algo for your equipment, then the profitability factors you provide in your password need to be the same denomination as the current estimate for the algo.

Here are the "current" profitability estimates for m7m and yescrypt:

m7m, 0.0733
yescrypt, 0.01403

Let's say you have an Intel Core i5-6600K. Your hash rates are as follows:

m7m, 69kH/s
yescrypt, 2.4kH/s

If you specify your password as m7m=69,yescrypt=2.4, this is the math that the stratum server does:

m7m, 0.0733 * 69 = 5.0577
yescrypt, 0.01403 * 2.4 = 0.033672

Well, m7m should be way more profitable for you than yescrypt, right? According to these calculations, you'd be making $0.38/day with yescrypt, but $56.57/day with m7m. Thus, the stratum server will keep you mining m7m all day long.

Except m7m is measured in MH/s, while yescrypt is measured in kH/s. So, you won't be making $56/day in reality. Thus, the correct password would be m7m=0.069,yescrypt=2.4. This give us:

m7m, 0.0733 * 0.069 = 0.0050577
yescrypt, 0.01403 * 2.4 = 0.033672

In reality, m7m is only going to bring you $0.06/day at that rate. Not $56. Then, yescrypt is more profitable at this point in time. And that's why right now, you see 21,000 miners on yescrypt, and only 634 on m7m.

This can be confusing because if you look at the chart on the website, m7m is listed higher in the table than yescrypt, because it's "current" estimate is a bigger number. But because they're measured using different denominations, yescrypt is currently far more profitable.