Yes, if one is playing on very large maps, with few opponents, frequent events, and abundant stars/abundant planets, then yes it is easier to max out every ideology Less so, if one isn't. 
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Instead of bringing subjective viewpoints to the table (including mine
), let's bring some cold hard data.
Doing a bit of a test right now, it appears that the Ideology Table follows a simple progression of +3 followed by a +2 followed by a +3 and so on for each trait that is chosen within a table.
Trait #1: 15 points
Trait #2: 18 points
Trait #3: 20 points
Trait #4: 23 points
To unlock all 20 traits in a table costs 780 ideology points. To max out all three would therefore cost 2,340 points (yes, I'm counting the disabled traits).
Checking the game data, random events give 10 to 30 ideology points, with 20 being the most common. So let's just use 20 as the baseline.
Near as I can tell from the data, planetary colonization is always a flat 10 points.
Now random events won't always give an ideological choice. I don't know what the frequency is, so I can't make any hard analysis on that. But lets say for arguments sake that one has 10 ideological random events in an entire game, for 200 points of ideology. Might be less, might be a lot more. That means, if one builds no ideological buildings, currently someone has to colonize 214 planets to get all three trees, presuming perfect ideological balance (which isn't likely due to distaste over choices). So lets bump it up a tad to 220.
What if I am vastly underestimating random events, though? As I said, I don't know what the frequency is, nor the length of some folks games. Completely fair point. So lets bump it all the way up to 1,000 points from random events. That'd be around 25 ideological random events (again centered around 20 points per event). That still means the player has to colonize 134 planets to max out all three trees, again presuming one doesn't build any ideological buildings and has perfect choice.
But what if a player DOES build them? Well then, everything gets thrown out the window since there is no current limit to building (some of) the ideological buildings other than players not wanting to "waste" tiles and the fact that only one of each type of building can be built on a single planet. Which almost makes this entire argument moot and then just gets down to how bloodyminded a player is to max things out. 
Still, looking at the data, I can see why some people are maxing out in what seems to be an easy manner in their eyes. Thing is, not everyone will be playing on the same settings, nor with the same playstyle. Some folks might be loath to waste what they see as precious tiles to use ideology buildings. Others might have more opponents than some people. And still others might play on maps that even though they are large, still wind up without many planets for one reason or another.
All that being said, I am still in favor of letting people choose the "pace" of ideological growth. Especially as more avenues of ideology come into the game. But I am wary of fixes like "number of planets" because then there is the point of "number of opponents". After all, an Immense map with fifteen, twenty, or more majors will play FAR different than one with eight.
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Naturally if one wants to "only" max out one tree because of immersion/RP, then it does become much easier to max out a single tree on larger maps. Even so, number of planets/opponents comes into play, I think.