Let’s break down what’s actually going on.

You’re not imagining it—there’s been a huge “sourdough everywhere” trend, and a lot of it is more cultural/marketing than technical necessity.

🧠 First: what sourdough is doing in these recipes

A sourdough starter is basically:

Wild yeast (leavening, but slower and less predictable than commercial yeast)
Lactic acid bacteria (acidity + flavor development)
A flour/water pre-ferment with enzymatic activity

So when bakers add it to cookies, muffins, cinnamon rolls, etc., it’s usually doing one (or more) of these:

1. Flavor complexity (the real reason)

Even in sweet doughs, sourdough adds:

Mild tang (balances sweetness/fat)
“Fermented” depth (more aromatic compounds)
Slight nuttiness over time

This is especially noticeable in enriched doughs like cinnamon rolls.

2. Texture changes (sometimes subtle, sometimes not)

Depending on how it’s used:

Long fermentation → more tender crumb (gluten breakdown)
Acid → can soften dough structure slightly
Pre-fermentation → improved keeping quality (slower staling)

But in many cookie/muffin recipes, this effect is often marginal or inconsistent because baking soda/powder is still doing the lifting.

3. Fermentation as a marketing identity

This is the big one.

“Sourdough” has become shorthand for:

“Artisanal”
“Slow fermented”
“More complex / handmade”

So even when the starter isn’t doing much leavening work, it’s used as a branding signal.

🍪 Why it feels unnecessary (your instinct is valid)

From a classical patisserie / yeasted dough perspective:

Cookies: already chemically leavened → sourdough is mostly flavor, not structure
Muffins: baking powder dominates → starter is mostly hydration/flavor
Cinnamon rolls: yeast already does fermentation → sourdough becomes optional complexity layer

So yes—many of these were excellent long before sourdough was added.

⚖️ When sourdough actually makes sense

It’s genuinely useful when:

You’re replacing commercial yeast in enriched doughs (long fermentation builds flavor)
You want partial fermentation for digestibility or texture change
You’re using discard to reduce waste (practical baking economy)

Otherwise, it’s often optional.

🧁 The honest bottom line

You’re seeing three overlapping trends:

Flavor experimentation (valid culinary exploration)
Waste-reduction baking (discard recipes) (practical)
Sourdough as aesthetic branding (the Instagram effect)

Only the first two are technically necessary. The third is mostly cultural momentum.

🧑‍🍳 One-line summary

Sourdough in cookies and muffins is usually there for flavor + identity, not because it improves the fundamental baking chemistry in a required way.