Exchanges have ‘listing fees’ for crypto-coins — I disagree with labeling this as bribing.

The assumptions that exchanges have to run nodes of all coins they list may not be true — they may use services of a commercial wallet provider for all of their customers. The wallet provider company is usually up to date with protection from threats.

Exchanges de-list coins because of zero or low trading volume for a significant period of time. Usually newly listed coins have high spread (difference buy-sell price).