This is a bit off topic, but why do I need a subscription to access a dictionary? How often should I be expecting the language to change? Not to mention that the UX got much worse since the 90s, when I had a program on my desktop to instantly look up words.
Language changes slowly but constantly: words evolve new sentences, new phrases are coined, others become less current. The OED is so big that the only practical way to revise it is continuously, a few entries at a time. Every quarter there are hundreds of changes: https://public.oed.com/updates/ . As with software, it turns out that financing a product that needs continuous updates is more effectively done with a subscription than by selling products as one-off transactions. (FWIW the print version of the 2nd edition OED is 20 volumes and is listed on the OED site at 860 quid.)
The OED is a historical dictionary that records over 1000 years of the language's development. It aims to be a complete dictionary of the English language from its origins to today. It frequently adds new entries and new examples of older words. I don't know that £100 per year is a reasonable price, but it's not an inexpensive endeavour to run; it employs many lexicographers.
Most people don't need the full OED and should probably just buy one of the smaller Oxford dictionaries. The Concise Oxford English Dictionary is an excellent single-volume dictionary of modern English based on the Oxford Dictionary of English (which is not the same as the Oxford English Dictionary. The OED is a historical dictionary, while the ODE is a dictionary of contemporary English).
