Table is parsed on block level. It can’t jump to inline mode before it detects cells layout. So, it only process backticks and escapes.
Since tables are not part of CommonMark spec, we follow GFM spec. You can check, github behave the same way.
In short: currently all backticks and pipe chars inside tables MUST be escaped.
If you wish different behaviour, you need to ask github guys to update spec. But, personally, i’m not sure if good resolutions possible at all on spec level. IMO this case is very specific, has workaround, and does not worth efforts to be spent for spec/parsers rework.