Andromeda - Where is everyone else?

So was just wondering, the only races we know of in the andromeda galaxy are the remnant, the angara and the kett. So where is everyone else? I know without mass relays that we're confined to a single star cluster but I would assume with billions of years of advancement without reapers, they would have invented a speedy way to get around andromeda, possibly without mass effect technology. 
In ME1, there were dozens of new races and also mention of previous extinct civilisations. 

So how come we've not seen nor heard of other races?

And this thread speculating about the writers thought process when coming up with the story and the number of races. Just saying the writers/ or bioware did it is the equivalent of saying god did it to explain everything about our universe and isn't really an answer.

Below is a lost of all known civilisations/beings in the milky way, many of which were in ME1

Sentient Milky Wayers                                                                      Sentient Andromedans

1)Batarians                                                                                               1) Remnant
2) Krogen                                                                                                  2) Angara
3) Asari                                                                                                     3) Kett
4) Turians                                                                                                  4) ???
5) Salarians
6) Hanar
7) Drell
8) Quarians
9) Humans
10) Elcor
11)Volus
12) Keepers
13) Geth
14) Collectors
15) Leviathans
16)Raloi
17) Reapers
18) Yahg
19) Vorcha
20) Arthenn
21) Thorian
22) Protheons
23) Inusannon
24)Oravores
25) Densorin
26) Rachni
27) Thoi'han
28) Zeioph
29) Zha'til

This was the E3 trailer of ME1 back in 2006. By the way, they seem to have brought back the 'tip of the spear' metaphor for ME:A when mentioning the pathfinder. In this trailer you see humans, turians, geth, salarians, asari etc