Accounting is concerned with past events and it requires consistency and comparability that is why it requires the accounting transactions to be recorded at their historical costs. This is called historical cost concept.
Historical cost is the value of a resource given up or a liability incurred to acquire an asset/service at the time when the resource was given up or the liability incurred.
In subsequent periods when there is appreciation is value, the value is not recognized as an increase in assets value except where allowed or required by accounting standards.