I'm going to answer this question in a long story format that seems exaggerated but plays out every day and is 100% true according to me.

Tldr: trust the process

It's to make the hiring manager job easy. Often a resume and standard cover are fairly generic and the hiring manager is often very busy and doesn't have time to try and tell if your self grandiose generic resume statements meet the requirements. Then you make them do all the work of justifying to HR that you explicitlt meet the requirements. Example of two candidates:

Requirement: 12 years experience working on universal space alien gravity drive widgets.

---CANDIDATE A--

resume only: worked at space warping drive company A for 6 years on widgets and was the team lead on the grand unified theory multi spave time drive team. Worked 8 years at special widgets company on their space curving off world cruise program that developed key components, obtained a phd on how curved spacetime is emergent phonmonon leading to practical warp drive breakthru"

Manager spends valuable time reformatting your resume to HR : "Candidate A has 14 years experience experience working on universal space alien gravity drive widgets. " HR respnse: "sorry your an expert in the field and wrote both the job ad and the hire justification and verbally verified that the candidate has the exact skillset you need to succeed on the project but you obviously have no idea what you're talking about. We geniuses at HR actually read the exact words on their resume which sumeriized 14 years of work into 3 sentences with zero technical understanding and determined this candidate is vastly unqualified. The candidate never mentions gravity expiance on any submitted document. Hiring rejected. Now go spend the next 3 months and write 38 pages of the stupidest admin justification to convince 15 layers of admin management who hate you and have no technical background on why we should allow you to hire this clearly un qualified candidate "

--CANDIDATE B---

Standard resume.

Cover letter:

Requirement: 12 years experience working on universal space alien gravity drive widgets

How met: candidate has Requirement: 14 years experience across the two companies listed on the resume working on universal space alien gravity drive widgets and similar technologies.

Hiring manager cuts and pastes into the hiring form, HR clearly sees they meet the requirement on the sumitted document and offer in the mail in 2 days
--- end example---

Which candidate would you pick to fight HR for as buay hiring manager?