Quick answer: unconditionally entering the battleground tapped will leave all of them at too great a drawback with respect to the other choices, that places are made for minimal play.
More specifically, there's essentially no benefit to utilizing Gates throughout the corresponding shocklands or core set/Innistrad duals; since there's which has no land type specific LD, gates tend to be for several practical functions strictly worse than their particular matching shocklands, because the shocklands could be fetched with Farseek and usually have the choice of coming into play untapped if you are willing to make the hit. Similarly, the core/Inn places tend to be the same as the Gates with the exception of the possibility of entering play untapped on turn 2+ (and keep in mind that the shocklands 'turn on' the core lands, which can be another point in shocklands' favor).
Between these two facets, the only thing that Gatelands have to offer over the other alternatives is little term: 'Gate'. If there have been cards that took real advantage of the gate type - say, something such as a Rampant Growth/Farseek for Gates - then I think you'd in fact see all of them benefiting from play in ramp porches. As it is, though, the only real cards that interact with Gates tend to be several creatures (nothing of which is within constructed-stats range) that gain little advantages for gates in play and Gatecreeper Vine, which fetches a gate but - regrettably - doesn't place it into play. This means the land kind (about for now) is not providing any upside to offset the advantages the other styles of dual have.
So why do they exist? Really, practically because you noted; RTR limited needs a substantial amount of manafixing since there are so many multicolor cards; this means placing repairing down into the normal slots. And even though Rarity is certainly not Power, WotC has actually several cause of not having rares 'outclassed' in significant means by commons, plus they've done hardly any powerful land rounds at common (or even uncommon) - you can easily typically anticipate that any land-based mana fixing that winds up within the common slot will likely be slightly poor.