Why do so many SaaS products build referral and loyalty systems from scratch?

I've noticed a pattern while building SaaS products.

Teams spend weeks (sometimes months) building features like:

• Referral programs

• Loyalty points

• Rewards

• Coupons

• Achievements & badges

• User levels

• Milestone rewards

• Cashback

• Fraud prevention for referrals

None of these features are the core product, yet every company seems to rebuild them.

It made me wonder:

Would developers rather have a single API that handles customer incentives, or do most teams prefer building these systems in-house?

I'm currently building Incenta, an API-first platform focused on referrals, rewards, loyalty, and gamification, so I'm genuinely curious how other founders and engineers think about this.

If you've built one of these systems before:

• What was the hardest part?

• What features ended up taking far longer than expected?

• Would you build it again, or use a managed platform?

I'd love to hear real experiences from the community.