It can be a bit easy to miss, but you're currently seeing the totals for the week, not all time. We do this intentionally because we think it's more valuable to see who's been active recently rather than the same 20 people who have the highest reputation all-time.
You can see the tab selections here:
What it took me time to realize is that not only are those users the top reputation earners for the week, that amount is the reputation they've earned so far this week.
If you'd like to see the total reputation of the top all-time users or the top users for longer periods of time, select them using the tab switcher.
Do note that these numbers are for fixed calendar dates, not a rolling month ("last 30 days) or quarter or year. This is why, currently, you'll see the same exact content on the month, quarter and year tabs. Being January, the current reputation earned for the month also represents the reputation earned by these users for 2019.