What Openreach provide for ISPs to order, and what ISPs then choose to offer to potential customers are two very different things.
Openreach are simply providing one underlying product with a few speed caps below the maximum. It used to be called "charging for facilities" or similar. Whether it still is I don't know.
ISPs have to look at the costs of providing backhaul for what are in mass-market terms extreme products, that are unlikely to have much take-up for at least five years. So not recouping the backhaul costs for a very long time. It is oft-publicised that most domestic users take the lowest fibre offering they can.
Medium-sized businesses act very similarly. Big business isn't in this market. They have specialist providers with specialist support and service guarantees. A few of those may already offer it, but they certainly won't be advertising where we might see it.
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