This is easily answered.
There is no reason for the innumerable multitude to be sealed because they are raptured and in heaven before the throne of the Father and pictured having resurrected bodies (see Rev 7:9–17).
There is zero biblical evidence that church saints will be on earth protected through the trumpet and bowl judgments. Rather, the evidence is clear that they will be in heaven before God’s wrath begins.
The 144,000 Israelites in Rev 7:3–8, on the other hand, are sealed for protection on earth during the day of the Lord’s wrath during the trumpet and bowl judgments.
They are not saved at the time of their sealing. They make up that final remnant of “all Israel” as first fruits (Rev 14:1–5), who will eventually at the end of the 70th week of Daniel will recognize Messiah and mourn, repent, and believe in Messiah.
The 144,000 Israelites in Rev 7:3–8 are chosen by God to be saved when the end of the seven-year period is completed, fulfilling Daniel’s 70 week prophecy of the nation of Israel when they recognize Jesus as Messiah. They are sealed for protection from the impending wrath of God (cf. Rev 9:4!) via the trumpets and bowls judgments.
Some may object that since the 144,000 are called “servants,” they must be saved at the point of their sealing. This is not the case. Robert Gundry has pointed out that this is not at all necessary and an assumption: “The designation ‘bond-servants’ (7:3) . . . anticipates their role in the reestablishment of the Davidic kingdom. Isaiah calls unregenerate Israel the ‘servant’ of the Lord (42:18–25) in anticipation of the nation’s restoration (43:1ff.)—exactly the interpretation here given for the 144,000 [see also similar anticipatory statements in, for example, Jer 1:5; Luke 1:15]” (Gundry, The Church and the Tribulation, 82).