It's true they don't pass to each other that often last season but I'm not sure where you got your numbers from. Before I get to that, we first need to look at things in context. There are mitigating circumstances for this.
RvP plays like an out and out striker and so spends most of his time up front receiving the final ball and shooting. Rooney plays a deeper role and spends more time in central midfield or areas outside the box.
With that physical gap between them, it is not surprising that chances for them to pass to each other are limited.
Not just that. United have focused on wing play (especially last season) and Rooney has specialised in distributing to the flanks. Especially long balls to the right wing. So with hardly any emphasis on creation through the middle and Rooney focusing on long balls to the flanks, is it any wonder they rarely passed to each other?
It's true their partnership is probably not the best in the league. I'm just saying they're not the worst. Their output together the last two seasons are still good after all. We need to stop with all this baseless exaggeration.
Now let's get to the numbers to get some perspective:-
2012/2013
Rooney & RvP
Mins per pass to each other = 7.95 (About 11 passes per 90 mins)
Assists created for each other = 4
Total Goals that season = 16 (Rooney) + 30 (RvP) = 46
Total Assists that season = 13 (Rooney) + 8 (RvP) = 21
Total = 67 goals and assists
Appearances that season GS(SB) = 31(6) + 40(8)
Rooney 0.78 goal incident per appearance. RvP 0.79 goal incident per appearance
2013/2014
Rooney & RvP
Mins per pass to each other = 10.68 (About 8 passes per 90 mins) (as at some time in March)
Assists created for each other = 4 (as at some time in March)
Total Goals that season= 19 (Rooney) + 18 (RvP) = 37
Total Assists that season= 17(Rooney) + 3 (RvP) = 20
Total = 57 goals and assists
Appearances that season GS(SB) = 37(3) + 23(5)
Rooney 0.9 goal incident per appearance. RvP 0.75 goal incident per appearance
Suarez & Sturridge
Mins per pass to each other = 8.83 (About 10 passes per 90 mins) (as at some time in March)
Assists created for each other = 6 (as at some time in March)
Total Goals that season= 31 (Suarez) + 21 (Sturridge) = 52
Total Assists that season = 12 (Suarez) + 7 (Sturridge) = 19
Total = 71 goals and assists
Appearances that season GS(SB) = 33(0) + 26(3)
Suarez 1.3 goal incident per appearance. Sturridge 0.96 goal incident per appearance
Just seeing the stats, we can infer a few theories and conclusions.
1) RvP missed many games last season and that is probably the main reason their goal and assist output was lower last season. If he had been fit, it would've pushed their stats closer to 2012/2013 territory.
2) Rooney stepped up to compensate for the loss of RvP but it wasn't enough.
3) Our obsession with a crossing game last season was probably the main reason their link up play was reduced
4) They're partnership exists and is not as shit as some people say they are
5) Suarez and Sturridge were really very, very good. (Obviously.

)
You are seriously going to insist they are the worst you have ever seen in your entire life? I guess you don't watch much football then. Whatever floats your boat, man.
But first I need to correct a few misconceptions.:-
1) Both of them playing centrally is not really an issue. Dwight Yorke and Andy Cole are proof of that. Many strike partnerships are like that.
2) While Rooney and RvP both play centrally, Rooney plays very deep while RvP plays up front most of the time. So they're not even covering the same areas of the pitch.
3) SAF did not pull Rooney down to midfield because the partnership sucked. That just doesn't make sense. He did that because we needed Rooney to back up the midfield as an extra man especially because many teams play with 3 in the middle these days. He's been doing that for quite awhile before that season.
Seriously, we really need to stop with the baseless exaggerations.