Why packages sources are NOT mirrored?

[Marcin Juszkiewicz]

                         My traceroute  [v0.85]
puchatek (0.0.0.0)                            Thu Sep 17 14:42:22 2015
Keys:  Help   Display mode   Restart statistics   Order of fields quit
                              Packets               Pings
  Host                       Loss%   Snt   Last   Avg  Best  Wrst StDev
  1. krzys.lan                0.0%    16    0.3   0.3   0.3   0.3   0.0
  2. 192.168.0.1              0.0%    16    0.6   0.6   0.5   0.8   0.0
  3. ???
  4. 89-75-11-97.infra.chell  0.0%    16    8.5   9.7   7.3  16.4   2.1
  5. 84.116.252.162           0.0%    16  224.2 220.9 218.1 227.2   2.4
  6. 84.116.252.174           0.0%    16  219.6 220.3 218.3 226.8   1.9
  7. 84.116.252.9             0.0%    15  223.8 221.4 219.9 225.0   1.5
  8. 84.116.252.41            0.0%    15  230.5 221.8 219.6 230.5   2.7
  9. 84.116.136.141          71.4%    15   44.0  42.3  40.7  44.0   1.3
10. 84-116-130-130.aorta.ne  0.0%    15  222.2 220.3 218.2 227.9   2.3
11. ch-zrh02a-ra1-xe-2-1-0.  0.0%    15  224.3 229.6 219.6 251.9  11.2
12. 84-116-130-125.aorta.ne 85.7%    15   42.3  41.5  40.8  42.3   1.0
13. 84-116-130-122.aorta.ne  0.0%    15  148.2 149.9 145.4 177.0   8.2
14. 84.116.133.158           0.0%    15  222.7 220.7 219.5 222.7   0.7
15. mpr1.sjc7.us             0.0%    15  222.5 223.3 219.4 253.3   8.5
16. ae9.cr1.sjc2.us.zip.zay  0.0%    15  249.4 225.0 218.8 249.4   9.7
17. v11.ae29.cr1.lax112.us.  0.0%    15  232.1 231.2 228.1 240.9   3.1
18. ae7.mpr3.phx2.us.zip.za  0.0%    15  242.7 239.8 236.5 249.9   3.5
19. 208.184.108.38.IPYX-072  0.0%    15  223.8 222.8 221.5 226.2   1.1
20. border1.po1-bbnet1.phx0  0.0%    15  221.7 222.2 220.7 226.0   1.3
21. redhat-2.border1.phx004  0.0%    15  226.7 224.8 222.0 238.2   3.9
22. tx-160-181-132-209.redh  0.0%    15  222.4 222.7 221.4 227.2   1.4
23. pkgs.fedoraproject.org   0.0%    15  232.3 225.3 222.6 232.3   2.7

This is my connection to pkgs.fedoraproject.org machine. Fetching 48MB 
archive reached 36% in 2 (two) hours...

We ship binaries through mirrors all around the world. yum/dnf knows how 
to use them to get packages in a quick way. Knows how to handle lack of 
connection etc.

But sources used to build packages came from one place. ONE...

Why? Why we are not have them mirrored?

Or if we have then which magic option I did not managed to find yet?