Just curious as to why not. Is there really that much difference between 10 and 19? Cowboys thought that Lamb was out of reach, but he wasn't. Draft is unpredictable, most people didn't see the Packers taking a quarterback in the first round, and by doing so that pushed someone else down the list, having more picks increases your chances of getting one of the top players.
If you think that after the top 12-15 the rest of the draft consists of only average or a bit above average players then you keep the 10 pick. Or if this is 1976 and you are a very good team that just needs the "cherry on top" player to get you to championship level, you keep it. But that's obviously not the case with the 2021 Cowboys.
But if you feel, as I do, that there are nearly always about 40-50 excellent prospects in the draft, this year being no exception, grabbing 3 in that range would make a world of difference to this team. Maybe not getting to championship level this year either, but it will mean a better chance at it....