As text values are stored as TEXT it's limited to 64kb of data per text field (incl. comment). That's too short for some use case like some java stacktraces.
Moving storage to MEDIUMTEXT would give us 16MB of data which should be enough for Java stacktrace. However, rendering pages with 16MB of data might be problem.
Arbitrary decision to block text and comments to 256KB of data, that's should be fine. It covers the reported issue (133KB java stack trace) and leave room for more fat inputs while keeping to something manageable for rendering.