Psalm 92:6–7 on why God causes the wicked to flourish.

Take note of what the Psalmist calls those who do not understand or accept this teaching. What room is there for those who insist on the so-called doctrine of ‘common grace’, which claims that God’s purpose for sending sun and rain is to bless its recipient? As clarified by the Psalmist here, the reason God prospers the wicked is to destroy them—reprobation.

6 The brutish man does not know,
and the fool cannot understand this.
7 When the wicked flourish like grass
and all the workers of evil blossom,
it is so they can be destroyed forever.
Psalm 92:6–7 (Lexham English Bible)

7 (6) Stupid people can’t know,
fools don’t understand,
8 (7) that when the wicked sprout like grass,
and all who do evil prosper,
it is so that they can be eternally destroyed,
Psalm 92:6–7 (Complete Jewish Bible)

7 ἀνὴρ ἄφρων οὐ γνώσεται, καὶ ἀσύνετος οὐ συνήσει ταῦτα. 8 ἐν τῷ ἀνατεῖλαι τοὺς ἁμαρτωλοὺς ὡς χόρτον καὶ διέκυψαν πάντες οἱ ἐργαζόμενοι τὴν ἀνομίαν, ὅπως ἂν ἐξολεθρευθῶσιν εἰς τὸν αἰῶνα τοῦ αἰῶνος.
Psalm 91:7–8 (LXX) [Corresponds with Psalm 92:6–7 in English Bibles)

Unfortunately, this emphasis of purpose is lost in many other English translations. The Septuagint uses the word ὅπως (hopos: meaning: that/ in order that/so that.) For further reading, refer to this article on Psalms 73 where the Psalmist explain that the purpose of the prosperity of the wicked is to set them on slippery places, and to cause them to fall into ruin.