Because the flow comes to them lol. There are 3 primary jobs on the trading floor: sales, sales-trading, and trader (risk taker). There’s typically 3-4 sales people per product on the institutional covering territories (e.g. g10 rates Asia or g10 rates west coast). Usually 8-10 sales-traders per product (in regions, so also g10 Asia etc). For trading there’s usually just 3 per product — London, NYC, and Tokyo.
Salesperson talks to customers all day and is very consultative. “You want to trade XYZ? What kind of payout are you looking for?” And they’ll help you figure out how to make a decent idea into a great trade (or that’s what they’re supposed to do!).
Sales-traders receive orders for customers. Can be through chat, phone, etc. Their job is to take orders and complete them within a very short timeframe (20 to 90 seconds is usually the benchmark). A big part of their job is figuring out the best way to get the order filled. If the security trades on an exchange, they can use electronic trading or an algo to complete it. If it’s more complicated, they’ll get prices from their traders, or others. Etc. These are the guys usually shown on a trading floor (because they’re loud, constantly yelling into their phones, and such).
Traders (risk takers) at a bank will use the banks balance sheet to warehouse risk that the buy side doesn’t want. Typically this is because of a mismatch in a mandate on the buy side — e.g. A value investor just wants to own value stocks and may sell some names that turn “growthy”. That’s an example of why buy side would want to off load risks that may still be ok/good. So the job of the bank trader is to look at incoming orders and see which ones they like the risk on (or if they want to do a favor for the customer). These traders are very smart and usually a bit more introverted in style, think google or Microsoft software engineers. They rarely yell and are typically the opposite of the salesperson (who is usually an Ivy League athlete lol, etc).
None of these guys are using technical analysis for trading decisions. Salespeople will use some TA charts to illustrate a point — e.g. “real rates have crept up due to fedspeak this week, hitting against the 50dma”. But these guys don’t trade, they just act as consultants.
Sales-traders may have “watch list” or “charts” open but purely for their own interest. When customers put in orders they’re pulling quotes off screens, and the “decision” factor is driven by bid/ask spread, what their trader is willing to do, and other items (stuff not on a chart).
Traders (risk takers), are looking at their portfolio mix (probably have hundreds or thousands of positions at any given time), analyzing risk, and making trades. Most of the risk work (if they like risk or not) and parameters are done pre market, and is updated for every trade they do and other large trades that hit the tape. Risk takers at the bank are the only ones who actually “hold” positions and take risk. These folks are acting as principals and are making a market for the trade.