go mod vendor does not pull packages to vendor folder

Question

Im coming back to golang after a couple of years and I've forgotten how go modules are supposed to work...

This is my main file - sync.go

package main

import (
    "database/sql"
    "fmt"
    "os"

    _ "github.com/jackc/pgx/v4/stdlib"
)

func main() {
    // urlExample := "postgres://username:password@localhost:5432/database_name"
    db, err := sql.Open("pgx", "postgres://localhost:5432/my_db")
    if err != nil {
        fmt.Fprintf(os.Stderr, "Unable to connect to database: %v\n", err)
        os.Exit(1)
    }
    defer db.Close()

    var result string
    err = db.QueryRow("select distinct name from my_table limit 1").Scan(&result)
    if err != nil {
        fmt.Fprintf(os.Stderr, "QueryRow failed: %v\n", err)
        os.Exit(1)
    }

    fmt.Println(result)
}

go.mod:

Have added the pgx lib by doing go get "github.com/jackc/pgx/v4"

module sync

go 1.17

require (
    github.com/jackc/chunkreader/v2 v2.0.1 // indirect
    github.com/jackc/pgconn v1.11.0 // indirect
    github.com/jackc/pgio v1.0.0 // indirect
    github.com/jackc/pgpassfile v1.0.0 // indirect
    github.com/jackc/pgproto3/v2 v2.2.0 // indirect
    github.com/jackc/pgservicefile v0.0.0-20200714003250-2b9c44734f2b // indirect
    github.com/jackc/pgtype v1.10.0 // indirect
    github.com/jackc/pgx/v4 v4.15.0 // indirect
    golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 // indirect
    golang.org/x/text v0.3.6 // indirect
)

go-sql on  master [+?] via  v1.17 
❯ ls                                                                                                                                                  
go.mod  go.sum  sync.go  vendor

go-sql on  master [+?] via  v1.17 
❯ cat go.mod                                                                                                                                          
───────┬──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: go.mod
───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ module sync
   2   │ 
   3   │ go 1.17
   4   │ 
   5   │ require (
   6   │     github.com/jackc/chunkreader/v2 v2.0.1 // indirect
   7   │     github.com/jackc/pgconn v1.11.0 // indirect
   8   │     github.com/jackc/pgio v1.0.0 // indirect
   9   │     github.com/jackc/pgpassfile v1.0.0 // indirect
  10   │     github.com/jackc/pgproto3/v2 v2.2.0 // indirect
  11   │     github.com/jackc/pgservicefile v0.0.0-20200714003250-2b9c44734f2b // indirect
  12   │     github.com/jackc/pgtype v1.10.0 // indirect
  13   │     github.com/jackc/pgx/v4 v4.15.0 // indirect
  14   │     golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 // indirect
  15   │     golang.org/x/text v0.3.6 // indirect
  16   │ )
───────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

go-sql on  master [+?] via  v1.17 
❯ go mod vendor                                                                                                                                       
go: warning: "all" matched no packages

go-sql on  master [+?] via  v1.17 
❯ ls vendor                                                                                                                                           
modules.txt

Why is my vendor directory empty ? What am I missing ?

If I try to compile, it fails as expected as my vendor directory is empty -

❯ go run sync.go                                                                                                                                      
sync.go:8:2: cannot find package "." in:
    /home/ninan/trials/go-sql/vendor/github.com/jackc/pgx/v4/stdlib