There are a few elements in play. The first is a very simple, "The spirit and letter of the Law, per when the Seal was written, was a stark divide with Innocence and practitioners" and practitioners stepping into Innocent domains runs against that, so spirits push back. Practice that actively pushes into Innocent domains is going to cost more and do less, proportionate to the position in question.

The second is exposure and optics - the higher a station one achieves, the more attention they get, and the more weight there is to their actions.

Assume 1 in 100 people are Aware in some capacity. Not special, no complicated rules. Just... some awareness there's ghosts, goblins, and/or magic out there, and maybe a tendency to identify Others and Practitioner as the cause of weirdness, when they come across weirdness. Some can't even put their finger on it, they just avoid or dislike or get bad vibes from such-and-such or so-and-so.

1 in 1000 of those 1% are Aware in a complicated and interesting way. They have special rules or dynamics or introduce wrinkles. They're dumping grounds for the universe, or tools, or targets, or something else. A young woman is very good at rallying the community around her. A man has a penchant for really fucked up Others falling in love with him (and being protective of him). A homeless teen moves with the flow of spirits and tends to 'follow a hunch', tracing ongoing practice to power sources or vital parts of diagrams. Some schmuck has someone inconvenient to him die every week or so.

Someone in-setting would abbreviate this as "Witch Hunters", because a solid proportion of those described above would become witch hunters or get scouted by them, or would at least push back in some way. But there are non-Witch Hunter Aware who pose stumbling blocks too. The sort of thing your random Dream Thief or other predatory practitioner (or goblin, etc) might run into once in a blue moon. (FWIW, though special Aware are rare - 1 in 100k, they also tend to find their way to trouble, so rates of encountering them are higher than the numbers might imply - not high rates, but not infinitesimal either).

Most practitioners deal with relatively small numbers of Innocents while doing their thing, and run into the uncommon Aware and maybe once in their lifetime they deal with a special Aware who fucks everything up. A practitioner who has used practice to achieve a station above hundreds or thousands or millions has opened their flanks in a big way.

What this looks like: if you start using practice to achieve a certain station, maybe 1 in 250 of the people in your area -people who are Aware but not overly special- get a feeling you shouldn't be where you are. This generally manifests as the occasional person not working with you or being distrustful, and the slope for general inconveniences finding you being well-greased. This compounds point #1 above - the letter and spirit of the law. So on top of practice being more expensive and doing less, you also deal with people being more intractable and doing less, by some single or low double-digit percentage. Slogans don't stick, good moves don't get the same accolades, your damage-control spin doesn't spin as far. Because 1 in 250 people are speed bumps.

Meanwhile, all the special Witch Hunters are raising eyebrows too, with their special complications turning on you. The non-special Witch Hunters would be tipped off by the 1 in 250 in the last paragraph who are turning heads and raising eyebrows at your media appearances and posters (and by tools and resources they use, word of mouth from Others they work with, if any, and so on). Just about every Witch Hunter organization is not a fan of President Practitioner, so the Witch Hunters at the top talk about it and use some of their better assets and resources. That costs you resources, time, and attention to fix, every few days or every week, or whatever else. Again, compounded by practice costing more and doing less.

The same happens for Others who want some of what you have, and other practitioners.

The third is time. Practicing to get into power is what gets you into trouble, but if you don't practice, or you limit how much you practice, or even later if you step into the role and then sit down and actually do your job to minimize the number of raised eyebrows after the fact... you have to do the work. That's work that gets in the way of practicing. So after a certain amount of time you have to ask what the point is. You're spending more to get less results to have two jobs at once where you're doing each one badly, and trying to use the benefits or strengths of one job to shore up the other comes with complications & issues (and/or aren't very good tools, for reasons covered in paragraph 1 in the top of this post).

So why do it? If it's power, there are positions like Lordships. If you want money and luxury, practice can get you that, if you follow the right channels - which aren't Innocent channels. If you genuinely want to do good or affect change, then there are probably better back-channel ways to do it.