Apologies for responding to this thread this far down the line, but I only now became aware that you had posted this question and noticed you hadn't gotten any answers thus far, so I decided to give answering it a shot.

Firstly, I’ll disclaim that I am from a country where metric is used and the sources I have access to partially refer to imperial units, so I may make mistakes.

That said, in 1950-51 Guatemala exported 6,900,000 stems of Bananas, which assuming an average weight of 88lb would be = 607,200,000 lb. or 5,983,445.01 Quintals (101.48lb) of Bananas. Total coffee exports are given as roughly 775,000 bags of 60kg each, so 102,514,830 lb. = 1,010,197.38 quintals. Thus, raw volume wise, Guatemala exported 4,973,247.63 quintals or = 504,685,169 lb. more Bananas then it did Coffee. And while that was quite a bit lower than the export of circa 900,000 bags of Coffee in 1948 and 1949 respectively, that still doesn’t come anywhere near banana exports.

Price wise however, coffee is the clear winner, and it’s not even close. Export prices for banana total $6,010,000 while for coffee total price of exports is $58,464,000. So, while bananas would have been the largest export by total volume, it was coffee that was worth far more during this period.

And yet, when we talk about PBSUCCESS we discuss United Fruit and its interests in bananas, not the pressure of the finqueros (Coffee planter class.) over coffee. So what gives?

Firstly, its important to note that unlike the banana export industry, which was largely constrained and dominated by United Fruit, who both operated its own company plantations and bought from other plantations, the coffee planters ran independent family estates. (Fincas) Thus while they represented an influential political and social class akin to a landed gentry, their divided nature and rural roots meant that they were isolated from the center of power in the capital. (Which is somewhat addressed in the CIA transcripts you link to.) And, in many cases, they had been isolated outright. Guatemalan infrastructure was so poor in the early 20th century, that into the 30s it was claimed that it was easier to reach Europe than the capital from the landlocked Alta Verapaz department.

Additionally, unlike the American dominated banana trade the Finqueros were usually of Guatemalan extraction, with the most common “foreigners” being assimilated Germans immigrants, some with roots dating back to the 1870s and 1880s. Thus, when any pressure they wished to exert would have to be done domestically, likely through the army. (Which many Finquero’s sons traditionally served in.) However, this alliance had largely been weakened since the start of an army reform and professionalization program carried on throughout the 30s, which had the unwanted side-effect of politicizing the Army, especially as instructors like Arbenz himself introduced ideas like Marxism to students at the Military Academy. Additionally, an abortive ouster of Juan José Arévalo by the more conservative members of the military (led by Francisco Javier Arana) in 1949 had failed and left the conservatives weakened. Arana himself had been killed and this allowed Arévalo and later Arbenz to conduct a reorganization and purge of the armed forces to oust opponents, including Carlos Castillo Armas. (Who ended up in exile.)

So, by 1950, the elite had already had their shot, Arana had blown it and the failed putsch had catapulted Arbenz into a position as the clear shot-caller in the armed forces, and likely the Republic as a whole. Thus, even though Decree 900 was opposed by the landowning class and any other bastions of conservatism within Guatemala they couldn’t do much about it. By the time it was introduced they did not have the strength to mount a counterattack and, given prior events, even their limited attempts at either opposing the decree or lobbying the government were severely constrained and viewed with immense hostility.

I've condensed a lot of issues for the sake of a relatively concise answer to your question, which I hope you'll have found useful. However if you want to ask a follow up on say UFCO, I would encourage you to do so, though it might take me a bit to respond.

Sources:

Dosal, Paul J. Doing business with the dictators: A political history of United Fruit in Guatemala, 1899-1944. Rowman & Littlefield Publishers, 1993.

Foreign Commerce Weekly. Washington: U.S. Dept. of Commerce, February 26th 1951. Print.

Foreign Commerce Weekly. Washington: U.S. Dept. of Commerce, October 29th 1951. Print.

Foreign Commerce Weekly. Washington: U.S. Dept. of Commerce, March 17th 1952. Print.

Grieb, Kenneth J. 1979. Guatemalan Caudillo: the regime of Jorge Ubico : Guatemala, 1931-1944. Athens, Ohio: Ohio University Press.

Gleijeses, Piero. "The Death of Francisco Arana: a Turning Point in the Guatemalan Revolution." Journal of Latin American Studies. 22.3 (1990): 527-552. Print.

PS. While "Doing Business with the Dictators" is implied to stop around 1944, for it and "Guatemalan Caudillo" its not a hard line, and they talk about the Ponce Vaides and even Arevalo presidencies to some extent.

EDIT: Since this post was brought up in the Sunday Digest, I gave it a second look to fix any grammar issues and improve clarity. If there's still some points that aren't clear I'd be glad to try my hand at answering followup questions.