It's really not though. I know the trade chart isn't the end all be all but a 3rd and a 4th gets you up there. Sounds steep but remember we're talking about a guy they have rated top 5 falling in this scenario.
just looking at some recent trades:
Philly moved up from the 12th pick to the 10th pick (Dallas) in 2021 for an extra 3rd rounder
Bucs moved up from 14th to 13th (49ers) in 2020 for a pick swap of a 4th for a 7th
Steelers moved up from 20th to 10th (Broncos) in 2019 for an extra 2nd and a future 3rd
Cardinals moved up from 15th to 10th (Raiders) in 2018 for an extra 3rd and 5th
Bills moved up from 12th to 7th (Bucs) in 2018 for a pick swap of 2 2nd rounders for a 7th
Rams moved up from 16th to 8th (Bills) in 2013 for a pick swap of a 2nd, 3rd and 7th for a (higher) 3rd
couple of notes -
1) you're right that it's not always a steep cost to get up there
2) there's not a ton of trades that happen in the sort of range we're talking about and that's possibly for a couple of reasons... lack of willingness of teams ahead to give up the chance at the guy they want and lack of willingness to give up picks from teams moving up for what may well be similar talent
you may notice the gap between 2013 and 2018 - not because i skipped any years lol - because not many qualifying or similar trades happened in those years - a surprising number of picks for players type trades but not a ton of mid-1st to higher-1st trades