Part of the market analysis involves understanding the "why" of where prices are going. If historical data suggests that prices are appreciating by 2% per month, we want to know whether it is appropriate to bring that same 2%/ month adjustment from the last sale pinpointed as holding that trend to the effective date, whether it is increasing from there, stabilizing, or even reversing. We can look at current inventory to assist, but we also have to make future predictions based on the best data available (or at least the best data known to the typical purchaser) to ascertain whether historical trends will hold on the current date or whether they change.
Not to mention, a 1-4 family residential income approach also utilizes pro-forma projections for a stabilized rent, which certainly qualifies as a prediction, albeit near-term. If we are to say that the income capitalization approach is forward looking, and consequently, utilizing predictions while the sales comparison approach is not forward looking, then there is an inconsistency in the valuation methodology.