为了回答这个问题，我们首先需要明确什么是"主力"。在股票市场中，"主力"是指对市场有较大影响力的投资者或机构。他们通常具备较大的资金实力，并且有着较高的交易活跃度。在交易过程中，主力投资者经常会选择拆单交易，也就是将大笔交易分成若干小单进行操作。

Why do main players split orders?

To answer this question, we first need to clarify what "main players" are. In the stock market, "main players" refer to investors or institutions with significant influence on the market. They usually have large capital and engage in high trading activities. During the trading process, main players often choose to split their orders, which means dividing a large transaction into several smaller ones.

主力之所以选择拆单交易，是出于以下几个原因。首先，拆单交易可以避免对股票价格造成过大的冲击。如果主力一次性下单交易大量股票，那么市场上的供需关系可能会因此而发生剧烈的波动，从而导致股价的大幅波动。通过拆单交易，主力投资者可以逐步吸收市场的流动性，减少对股票价格造成的负面影响。

There are several reasons why main players choose to split orders. Firstly, splitting orders can avoid excessive impact on stock prices. If main players place a large order for a substantial amount of stocks at once, it may cause significant fluctuations in the supply and demand relations in the market, resulting in a sharp volatility in stock prices. By splitting orders, main investors can gradually absorb market liquidity and reduce negative impacts on stock prices.

其次，拆单交易可以降低交易成本。股票市场中存在着一定的交易费用，如佣金等。而高频率、大额度的交易往往需要支付更多的交易费用。通过拆单交易，主力投资者可以分散交易量，并在不同价位上进行操作，从而降低总体的交易成本。

Secondly, splitting orders can reduce trading costs. There are transaction costs in the stock market, such as commissions, etc. High-frequency and large-volume transactions often require higher transaction costs. By splitting orders, main investors can distribute the trading volume and operate at different price levels, thereby reducing overall trading costs.

此外，拆单交易还可以利用市场波动性获得更好的交易机会。在股票市场中，价格波动是非常常见的现象。通过拆单交易，主力投资者可以根据市场的波动性调整交易策略，以获取更好的买卖时机和更优的交易价格。

Furthermore, splitting orders can take advantage of market volatility and seize better trading opportunities. Price fluctuations are common in the stock market. By splitting orders, main investors can adjust their trading strategies based on market volatility to obtain better buying and selling timing and better trading prices.

综上所述，主力投资者选择拆单交易是为了避免对股票价格造成过大的冲击，降低交易成本，并利用市场波动性获得更好的交易机会。对于普通投资者来说，了解和理解主力拆单交易的原因，可以帮助他们更好地分析市场行情，制定合适的投资策略。

In summary, main investors choose to split orders to avoid excessive impact on stock prices, reduce trading costs, and take advantage of market volatility for better trading opportunities. For ordinary investors, understanding the reasons behind main players' split orders can help them analyze market trends better and formulate appropriate investment strategies.