Because they're ruthless and proud.
Same reason they keep trying to score as many goals as possible when they are already 4 goals up.
I think they did care enough to:
1) win
2) at least not get humiliated with a 6-0 thumping.
Before the game maybe. But consider the density of international matches + club fixtures being every 3 days, as soon as conceded 2-3, why keep going when a) you can achieve qualification in the other set of fixtures against shittier teams ; b) you're guaranteed a seed in the semis for the qualifier playoffs as a runner-up?
In the event of a win, they would have won the group and qualified for WC 2022 automatically, yes. (Edit: no they would not, ignore me) But there's at least 2 other chances to do so and it's the middle of a pandemic. I bet my left nut every big nation has people calculating these permutations and feeding them to managers.
Also why the fuck are federations still scheduling friendlies?
Since 2018:
Autumn 2018 - 4 Nations League matches + 2 friendlies
Spring/Summer 2019 - 2 qualifiers in March 2019, 2 in June
Autumn 2019 - 6 qualifiers
Spring/Summer 2020 - 3 friendlies planned for March and June 2020 ahead of Euro cancelled
That adds up to 19 matches, 14 competitive
Now cue 2020-2022 cycle:
Autumn 2020 - 6 Nations League + 2 friendlies
(already 180 minutes more football than needed)
Spring 2021 - 3 qualifiers
Autumn 2021 - 3 qualifiers in September, 2 in October, 2 in November = 7 total
PLUS 1 UNL semi + 1 UNL final/third place
Spring 2022 - 2 WC potential playoffs matches through qualifiers + 2 through UNL
Winter being the world cup
16 competitive matches minimum
How many friendlies we gonna get here?