The core technical reason is blockchain throughput and latency. A social network's most frequent operations — rendering feeds, loading post bodies, delivering media, running full-text search — require sub-second response times and handle millions of reads per second. No current blockchain, including Polkadot parachains, can serve that volume at that speed. Block finality on Polkadot is roughly 12–18 seconds, and even optimistic parachain block times sit around 6 seconds. Every post, every scroll, every image load as an on-chain transaction would make the UX unusable compared to what people expect from X, Instagram, or WhatsApp. Storing rich media (images, video, documents) on-chain is economically prohibitive — the cost per byte of on-chain storage is orders of magnitude higher than a CDN or object store, and blockchains are not designed for content delivery at scale.

The second constraint is state complexity and query flexibility. A social platform needs relational queries: "show me all claims related to this story, sorted by most recent signal, filtered by collective verdict status." Blockchains store state in Merkle-trie structures optimized for cryptographic verification, not for ad hoc filtering, full-text search, or aggregation. You'd need an off-chain indexer anyway (like SubQuery or a custom GraphQL layer) to make the data queryable — at which point the indexer is your Web2 backend, and the chain is just the source of truth for a subset of records. Going pure Web3 doesn't eliminate the server; it just hides it behind an indexing layer while adding latency to every write.

The third reason is identity UX and onboarding friction. Pure Web3 requires users to manage wallets, sign transactions, and pay gas fees. For a civic-information platform targeting journalists, activists, and everyday citizens in Latin America — many on mobile, many unfamiliar with crypto wallets — that friction is a hard adoption barrier. The Web 2.5 approach lets you offer familiar email/password or social login for the fast-path experience, while using DIM proof-of-personhood as an opt-in integrity layer. Users get verified-human status without needing to understand key management, and the blockchain proof is anchored behind the scenes rather than blocking the signup flow.

What you actually need from the chain is a narrow but critical set of guarantees: immutable commitment of claim/signal/verdict hashes (so evidence trails can't be silently altered), decentralized identity proofs (so verified-human status can't be revoked by a single operator), and governance records (so collective decisions and methodology changes are auditable). These are low-frequency, high-integrity writes — exactly what blockchains are good at. Everything else (the social graph, content delivery, search, media, notifications) is better served by conventional infrastructure where you can optimize for speed, cost, and developer productivity. The Web 2.5 split isn't a compromise — it's using each layer for what it's technically best at.