Politics is hard. Government spending is death by a thousand cuts, so the easy things to do are two: remove whole departments (remove all of the education, veterans, and defence, that will net you 1.5T) or ask the heads of each department to do the cuts. But then each one will face the same issue, and the deeper you go, the more you encounter people who want a specific spending e.g. reps who got elected supporting veteran support or education spending or a specific factory in Springfield, Illinois.
People favor spending cuts the way they favor tax breaks: don’t cut you, con’t cut me, cut that fellow behind the tree.[0] everyone's is for them in the abstract as long as they don't touch them.
And yes, I think the richest man in this world does not know how federal funds are being spent, based on the fact that he thinks he can cut "at least 2T" out 6.5T. To save 2T you'd have to erase the Department of Health[1]. If you cut 50% of Social Security, Health and Defence, you'll not get that, and people will riot.
Also, I point you to X, where Musk managed to save money by firing 70% of the workforce and <checks notes> losing 80% of the company value. The fact SpaceX and Tesla are successful[2] does not automatically translate in Musk being good at everything.
[0] https://quoteinvestigator.com/2014/04/04/tax-tree/ [1] https://fiscaldata.treasury.gov/americas-finance-guide/feder... [2] both, let me point out, with massive help from government expenditures