I will list the reasons for you below immediately...
Right, Paolo would lend me his Steinway and it's not the first time he has lent it to me to play and record on if that is what you mean, and I take this opportunity to thank him publicly. However, speaking of libraries, I must tell you that an expert ear will notice anyway; I am talking about someone who knows their stuff, has heard practically all of them, and works with them. I must tell you that I would have considerable difficulty recognizing East West...
There are, however, some technical, qualitative, and economic issues linked to each other that make me opt for recording with a library rather than in a studio or at home...
At the same level of quality and sound output, library vs. acoustic recording:
To obtain the same sound you would get with those libraries, you would need microphones costing at least—and I emphasize AT LEAST—1500 euros each, and a normalized location. By normalized location, I mean a room completely covered in wood or sound-absorbing material. You might say: there are pianists who go to record in temples on top of mountains, true; I'll answer you, those techniques exploit the natural reverb of certain ancient buildings. In this way, everything sounds more natural, even though nobody does this nowadays since amazing convolution reverb machines are available on the market. This is why pianists now only record in studios and no longer in the temples of music (the great concert halls)...
Even the price for an excellent convolution reverb exceeds 2000 euros. To this, we must add excellent tube preamplifiers; here we are around 4000 euros for a two-channel setup. A digital mixer for volume management and pre-equalization, a computer, and finally, a vast amount of knowledge to make everything work and to perform post-production. The total? I haven't done the math, but I believe we are approaching 10,000 / 12,000 euros!
One might then think about recording in a studio. To record in a studio equipped with a Steinway (there are some in Rome), it costs 250 euros per day for last-minute offers (studios that work hard to ensure the studio is busy on a day without appointments offer last-minute deals with rock-bottom prices); otherwise, normally a studio would charge you 150/200 euros per hour to record. Mastering excluded, therefore...
Are digital samples used because errors can be corrected? Well, I would say absolutely not; I mean, errors can also be corrected with audio recordings—you do takes of various phrases and take the best one by copy-pasting and cross-fading. It's easy to understand why in old records there were clearly errors and in today's there isn't even a trace of them. So, were pianists in the past bad and those today geniuses? I don't think so at all; it was simply that back then it wasn't possible to do these tricks. You could cut and edit entire sections of a Beethoven sonata, but not a single phrase. Therefore, regarding the error argument, it seems obvious to me that it is not the reason why one turns to samples. Obviously, recording live in a studio is a beautiful experience, but with these prices!!
The choice of the perfect sample is therefore fundamentally determined by only one factor: convenience. One looks for a sample that is indistinguishable from an acoustic performance in a studio. This way you save a ton of money, no one notices you didn't play on an acoustic piano, the output is perfect, and above all, nothing changes with the studio recording: as many errors as you make with samples, you fix them; as many errors as you make in the studio, you fix them. What changes is the money left in your pocket, and if we want to talk about the environment, but if we are talking about audio recordings and not video, I ask you: what do you think changes?