The exception are those who have electricity included in rent, hence why "unprofitable" miners still sell for a good amount. There is a point, however, beyond which the miner is unlikely to pay its initial cost in any reasonable time. Thus, the best case scenario is a miner that has already paid for itself and is located where it costs nothing to run nor is it tying up resources that are better used to run newer miners.
All in all, altcoin mining is a lot more attractive for beginners.
I hear what you saying but eventually even using free electricity will cost more then you make. For example let us say you have 1000watts worth if mining machines and your landlord is fine with that. You add another 1000 and the landlord tells you to please try not use any more. There you have reached the limit. No such thing as free anything. You can't have like 10kw of machine running because they were the first ones made. No landlord will allow it without putting the price up. So ya eventually scraping them is the best thing to do or using them as a learning device or perhaps get in very very early with sha256 altcoins. Bit good luck with that seeing as you can rent massive hashrste for a few hours just after the coins oqunh which makes keeping older minder complete counter productive. Plus there is still the heat they generate.
However.. to increase the shelf life people in cold countries can use them instead of heaters and pay less then running a heater. It still runs at a loss but now it's a heater not a miner. I think having some miners as house hold heaters is really cool idea and so hitech and totally geek. Everyone will.envy you
Or simply as a decoration or reminded of the old days of mining.
Hence the "not tying up resources for better miners" part. If the limit is, say, 2kW and you already have 2kW of miners, you'll have to remove at least 1kW of miners to add 1kW of newer miners.
A friend of mine actually did use an Avalon 4 as a heater. She was sharing a house with one or two others, so her effective electricity cost was 1/2 or 1/3 the usual rate. She was used to hot weather and liked her room much warmer than most people do. One of her friends sold her a Bitcoin miner and provided help on setting it up. The net result was that she had a machine that kept her warm and helped pay for her medical school expenses.
A college student today would be much more likely to go with altcoins after considering that the really profitable miners are really expensive and really noisy, GPUs have many other uses, and GPUs resale better. Not to mention that "winning" is no longer "paying back the full price of the miner that has no other uses" but rather "getting a meaningful discount on a PC that would be bought anyways".