How so?
There are two struggles that I have noticed.
First, Catholic spiritual practices always feel optional in low-church Protestant spaces. Again, some of this is due to the cultural allergies I've already described. But I think the deeper issue concerns how Protestant spaces, by leaning so heavily into justification, never turn to emphasize the role of sanctification in salvation. Consequently, anything introduced downstream from our "being saved" feels like an optional add on. You might introduce contemplative prayer to your church, but there's a widespread assumption that you can opt out if you wish. You can start celebrating Lent at your church, but members participate only if they want to. We can encourage you to adopt a rule of life, but it is only a suggestion.
This has been my experience in sharing Catholic practices in Protestant spaces, a general vibe of "Let me share with you this ancient practice which will deepen your relationship with God. But you don't have to do it if you don't want to." Spiritual formation feels like a hobby, something you might dabble in a little bit. But nothing pressing, urgent, and necessary.
To be fair, it's not like every Catholic engages in all these practices, or that Catholics are better formed than Protestants. My point is simply to note that when you plant practices aimed at sanctification in soil that has privileged justification it shouldn't be surprising if those practices are met with widespread indifference. Spiritual disciplines just don't feel necessary. So we share them in Protestant spaces with a "try it if you want to" attitude.
The second struggle is related to the first. If you do try to push harder on the adoption of spiritual formation practices, if you start shifting away from "optional" to "necessary," you're going to get some pushback. Spiritual formation as "necessary" triggers concerns about "works-based righteousness." Concerns will be raised about Pelagianism, that anything that feels "effortful" and requiring of "discipline" is starting to overemphasize human agency over the regenerative work of God. The monergism versus synergism debate resurfaces. When push comes to shove, low-church Protestants default back into revivalism over discipline when they desire spiritual transformation as the former emphasizes the work of God and the latter human effort. To my point, revivalism better fits Protestant soteriology than does a vision of spiritual disciplines.
In short, you're damned if you do and damned if you don't. If you can't say spiritual formation is necessary, that sanctification is as important as justification, then spiritual formation becomes optional and people engage with these practices in a disjointed, hobbyistic, do-it-yourself, opt-in/opt-out approach. As a consequence, spiritual formation never becomes a shared cultural ethos nor gains collective forward momentum. We share the exotic fruits of the ancient tradition, but those plants never take deep root.
