Offering things free is only generous if they have a resale value, which much old furniture does not, and if the owner can be bothered to list it and package it or otherwise arrange delivery to the customer. As often as not, someone coming to get it is doing the owner a favour by removing the need to get rid of it themselves - few charity shops will now accept furniture or large items. A lot of people willing to take used furniture with no value will not have spare money. If they did they would buy new. The chances are higher than average, therefore, that they won't have transport, and if hiring a van will cost more than the item is worth (very probably, if it is being offered free of charge) then it's not worth it.
It is different if the item is a carriage clock or a vase - something that could be carried home by the taker or taken to a charity shop by the owner - but even then there is effort attached if the owner would prefer the item to be used and not clog up landfill.
We had a big clearout a couple of years ago, renovating some rooms and decorating everywhere. Quite a few items had to go to make way for new ones. I listed them on a local site and stated 'collection only', as the larger things needed a van rather than a car (eg a sideboard). There were two wingback chairs that had to go too. Someone took one, and a young woman came to see the other and loved it, but as she had a small car it wouldn't fit in the back. Mr D's car is quite large, so we dropped the back seats and put it in there and delivered it (about 8 miles). Why wouldn't we? The alternative was to take it to the tip or have it under our feet until someone with the means to take it home took it away. I also had a lot of adult colouring books and pens which someone wanted for a care home, but they were too heavy for her to take on the bus. Again, dropping them off was much more sensible than disposing of them.
I know what people mean about the tone of replies though. I have had some quite dreadful ones. I offered a free microwave and one reply was just 'Address?' before I'd even agreed that he could have it. I had given the area in the listing, so it's not as though he was working out whether he could get here or not.
Another time I was getting rid of a vacuum cleaner and a woman messaged to say 'If you take it to X shop at 6.00 I will get it from you there.' No 'please', 'thank you', or 'would you be able to?' If she had said she didn't have a car but would love the cleaner, so would I be able to get it to her then Mr D would have taken it happily. No more effort than taking it to the tip, which would be a shame, as it was fine - I was just replacing it with a cordless model. As it was, I was annoyed by the tone and we eat at 6.00, so I said no. There were others interested anyway.
Don't get me started about the 'no shows' and the 'grabbers' though. Our local site has started to ban those who say they want something then don't collect it as arranged, and those who never give anything but take more than three items a week. There are definitely people who have alerts set when items are listed, and pounce on far more things than one person could possibly need for personal use. That is not the purpose of the group, which is to pass on and reuse things that would otherwise be wasted. It is meant to be collaborative, not grasping.