It's far from being exhaustive, but there's some elements that might provide an answer there (I'll copy some parts): roughly, conquering Germania would have been relatively too costly for dubious immediate gains.

Contrary to Gaul and southern Britain, most of Germania's people kept a pastoral way-of-life, with a relatively economically underdeveloped outlook. What factored in Augustus' motivation to plan and enact an important campaign in Germania were less hoped material gains to be obtained there than stabilizing the border regions and put an end to Germanic mercenariate and raiding in Gaul in order to pacify these new provinces.

The policy of establishing client states (as in Gaul before Caesar, or in Britain under Caesar or Augustus) wasn't so obvious in Germania where simpler societies prevailed, unified from time to time under prestigious leadership (Teutoni or Cimbri; or Ariovist's Suevi) but seemingly unstable and limited in time; so a direct approach was elected by the emperor : it's not clear to us how far he intended to advance, and it's quite possible nobody really had a clear cut idea then, the idea of reaching the Elbe being more about Roman prestige than an innate benefit.

The campaigns were no military promenade (Arballo being sort of an "almost" Teutobourg), with harassed troops, lengthy occupations, not so reliable peoples (no real equivalent of Aedui, as a powerful polity acting as Roman political and logistical support) and while imperial communication maintained a face of everything being under control, that was really shattered after the disaster of Teutoburg; where decades of harsh and costly war (military and logistic wise) for a really dubious and superficial political gain made it clear that subduing Germania would require a lot more men and resources, especially considering that supply had to come from Gaul.

It would have required building or rebuilding infrastructure from scratch if the limes was to be set on the Elbe, whose strategical relevance was meager. While the Rhine itself was directly supplied trough the old Rhone/Saône trade road (the same that fueled Caesar's war effort) , benefited from a strong agricultural production to supply armies with Romans could directly use pre-existing Gaulish road network at this end; nothing of the sort really existed along the Elbe, firmly set in the pastoral, less developed, more swampy and foresty part of Germania.

The problem was less how to expand the Roman border and more "why", pretty much as it happened for northern Britain where most of modern Scotland was subdued but quickly (if gradually) abandoned during the late Ist century CE because it would have involved too much military and fiscal expenses best used elsewhere : eventually Germania Inferior and Superior were carved out of Roman Gaul (rather than being "lost", these were post-Teutobourg creation as militarized provinces).

Interestingly, while failed, Augustean campaigns had the benefit allowing Romans and Germans to directly interact with each other, to create a net of obligations, trade, alliances, etc. that outlasted the abandonment of the lands beyond the Rhine. Romans products could be found in the region trough state-backed trade and gift-diplomacy, further trying local chiefs to a Roman alliance against other German or to obtain the goods Romans were interested in. As much Germanic auxiliaries or mercenaries were recruited in the Roman army still after Teutobourg; Romans advisors were sent in Germania (as far as modern Poland) as well. Basically, Rome went trough its usual policy of client chiefs to stabilize the border, at a more limited cost (even if military intervention beyond the Rhine and Danube still regularly took place, if more to "police" things up than outright conquest).

Everything that Romans could have taken from conquest could be taken from a trade happening in a dominant-dominee situation across the border, furs, amber, salt, slaves and eventually grain as "outer" Barbaricum, with the political stabilization and the border-crossing of Barbarians as seasonal or permanent migrants (working in fields or military service) made the right-bank of the Rhine quite possibly not that different from what existed in Roman Germania and an attractive and developed region of its own (which, interestingly, might be one of the motivation why the Agri Decumati were taken over in a later period).

Finally, the Rhine was far too convenient as a border, both strategically and logistically; while what Romans would have to pay up for conquering and provincializing Germania was certainly going to be extremely costly for dubious gains that they could get from political and military influence over Barbaricum.