Maybe they don't have data for people making more than that? There are relatively few people with incomes that high, and their time is probably valuable enough that they're disinclined to waste it filling out happiness inventories.
If we ignore many countries where $128K+ is quite rare, at least. In the US, about 14% of the households earn that much or more. However, the breakdown is more interesting here: Only ~1% of households in the US earn between $125-130K, compared to ~5% earning between $35-40K. The groups do become quite a bit less representative as you climb the income scale.
Maybe they don't have data for people making more than that? There are relatively few people with incomes that high, and their time is probably valuable enough that they're disinclined to waste it filling out happiness inventories.