Why can't lightning network channels increase balances？ If A and B have a Lightning Network channel，it was opened with a funding transaction (say, 1BTC from both sides for 2BTC total).  After A has spent some time transacting with B, the balance of the balance of the channel will be spent and then the channel will be closed with a confirmation transaction. Why doesn't the Lightning Network support additional funding transactions within this existing channel so that A and B can continue use this channel for transactions?
Any additional funding transactions would not be covered by older commitment transactions which can result in the loss of funds. Older commitment transactions will not contain inputs that spend from the new funding transaction. The funds sent in the second funding transaction require B to sign a spending transaction, and if B refuses, then A has no way to get those funds back should an older commitment transaction be broadcast.